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jimh posted 02-22-2004 11:20 AM ET (US)   Profile for jimh   Send Email to jimh  
Please use this message thread exclusively for questions related to the material in the Reference Section article

A Primer on Primers

This article discusses the proper installation and operation of the primer bulb in fuel lines used with outboard motors.

David Livingstone posted 02-23-2004 04:29 PM ET (US)     Profile for David Livingstone  Send Email to David Livingstone     
Great article Jim. I once got back to shore using a part of an inflatable ballon jammed in to replace a bad o-ring in the fuel line.

All the Best, David

WhalerAce posted 02-25-2004 10:28 AM ET (US)     Profile for WhalerAce  Send Email to WhalerAce     

Great Article, as usual.

One thing I am still curious about, though, and that is the propensity of riggers to want to mount the primer bulb so close to the END of the fuel line (that is, by the engine). It seems to me, intuitively, that the proper place to mount the primer bulb would be as close as possible to the outlet of the tank. This way, you are PUSHING fuel along the fuel line, not pulling it.

I had a case the other day where I could not prime the port engine on my Temptation. (The Temptation underneath the deck looks almost exactly like my Outrage with Whaler Drive did -- by that I mean that coming from the underdeck tank there are two large hoses that run to a transition plate. At this plate are bulkhead fittings that convert the fuel lines to the black 3/8" hoses that then run to the fuel-water separators and filters, and from there to each respective engine). I could pump and pump, but could never get gasoline to flow. I tried all of the usual tricks to make it work (yes, checking orientation of the bulbs, checking for air leaks, etc).

Finally turned out the easiest way to resolve the problem (which mainly showed up of the first start-up of the day) was to add a "primer" primer bulb just a few inches past the previously mentioned transition plate. This allows me to fill the separators and filters with gasoline (and not have to create a vacuum to do it) and get gasoline to the engine filter/carb/whatever with a whole lot less squeezing. I can then reach over the WhalerDrive and prime the last bulb as usual.

I would still like for someone to explain the rationale of pulling the fuel via vacuum versus pushing the fuel from the closest point to the tank.

I appreciate the indulgence.


jimh posted 02-26-2004 09:43 AM ET (US)     Profile for jimh  Send Email to jimh     
I don't have a good answer for you, Ace. On boats with internal fuel tanks—and this is becoming more common these days even on smaller boats—it does seem that the most common place to find the primer bulb on a pre-rigged boat is at the engine. This may also be due in part to the fact that many engines now do not come with a fuel line connector on the cowling, but instead are just provided with a short length of fuel hose dangling from the engine. The rigger has to splice this to something, so it makes a natural place to insert the primer bulb.

If the primer was not placed there (on these boats with no fuel disconnect at the cowling), they would have to insert a splice and put the primer somewhere else.

I'd be interested to hear more conjecture about best placement.

ibeenfishing posted 02-24-2004 05:09 AM ET (US)     Profile for ibeenfishing  Send Email to ibeenfishing     
I have a new uninstalled Pate 27 gal. tank and a new OMC gas line. It seems no matter how I mount the gas line the primer bulb will not be pointing skyward as Jimh's new article suggest. The bulb will either be pointed down on the front side or the backside of the tank.

Should I do surgery on this new gas line and try to relocate the bulb closer to the engine?

daverdla posted 02-24-2004 07:11 AM ET (US)     Profile for daverdla  Send Email to daverdla     
I moved mine closer to the engine two years ago. Simple job. I like getting the bulb back there out of the way.
bloller posted 02-24-2004 06:15 PM ET (US)     Profile for bloller  Send Email to bloller     
I moved my primer bulb nearer to the engine and pointing upward as well. It solved a fuel delivery problem I was having on my new outboard.
Steve Leone posted 02-27-2004 01:56 AM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
Coast Guard Requirement. The primer bulb must be placed over the outboard well. If it is "inside" the boat it does not meet the requirements for the "two-minute" burn rule. These regs were set in place to give a boater 2 minutes to either jump out of the boat or grab a fire extinguiser real fast, I guess. Fuel line is sold with the same ratings. Also, double hose clamps at all junctions plus an anti-siphon valve at the tank for inboard tanks (why not carry-ons?). Steve
jimh posted 02-27-2004 08:15 AM ET (US)     Profile for jimh  Send Email to jimh     
The regulation cited below does not mention double hose clamps.


I have read most of the regulations regarding fuel tanks (see below) and I don't see a mention of a "two minute burn rule."


I would appreciate if the applicable federal regulation could be cited that requires double hose clamps and describes the "two-minute burn rule."

Also, all of section 33 CFR Part-183 Subpart J Fuel Systems is not applicable to outboard powered boats. I reproduce 33 CFR 183.501 (emphasis added):

[Code of Federal Regulations]
[Title 33, Volume 2]
[Revised as of July 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 33CFR183.501]

[Page 851]




Subpart J--Fuel Systems

Sec. 183.501 Applicability.

Source: CGD 74-209, 42 FR 5950, Jan. 31, 1977, unless otherwise


(a) This subpart applies to all boats that have gasoline engines,
except outboard engines, for electrical generation, mechanical power, or
(b) [Reserved]

[CGD 74-209, 42 FR 5950, Jan. 31, 1977, as amended by CGD 81-092, 48 FR
55736, Dec. 15, 1983; USCG-1999-5832, 64 FR 34716, June 29, 1999]

A two and a half minute period is specified in a Fire Test procedure for components of the fuel system of boats using gasoline engines (except for outboard boats) in 33 CFR 183.590

However, I do not see anything in there that would constrain the mounting location of a primer bulb.

jimh posted 02-28-2004 08:27 AM ET (US)     Profile for jimh  Send Email to jimh     
[Joined together two threads on this topic that were running concurrently.]
Chuck Tribolet posted 02-28-2004 08:30 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
ibeenfishing, just give it a little slack, and turn it to
point up while you pump it.


jimh posted 02-28-2004 04:12 PM ET (US)     Profile for jimh  Send Email to jimh     
Another thought on primer bulb placement:

If the primer bulb were placed upstream of the fuel/water separating filter, you could pump the primer until firm but not be delivering fuel to the engine. A blockage in the filter could be preventing the fuel from flowing to the engine, but you would not have an indication of this from the behavior of the primer bulb.

If the primer bulb is close to the engine and you have filled it with fuel by squeezing, you can be reasonably certain the engine is being supplied with fuel. If there is a blockage downstream from this point it is probably under the engine cowling.

Other comments or ideas about optimum placement are welcomed.

SpeedBump posted 02-29-2004 09:32 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
I have three different gas lines for various boats, two whalers and one for a sail boat auxillary outboard. All lines are used on portable tanks ranging from 6-12 gals. Two are OEM lines and one a tempo retrofit. All three have the short length of fuel line to the primer bulb from the fuel tank then a long length of fuel line to the outboard. the arrow on the primer bulb shows the flow of fuel from the tank thru the short length of fuel line to the bulb then out to the outboard.

This is contrary to the "ideal" set up that JimH references in his articles. This set up also allows the line to be primed from the helm rather than at the out boards which seem safer in the event you must change lines on the tanks or a connector comes loose from the tank while underway, all that have occured at least once each season.

So, I must admit I am a bit confused on wheather or not to change my current set ups. Are OEM fuel line assemblies now made according to Jim's referenced article?

jimh posted 02-29-2004 09:46 PM ET (US)     Profile for jimh  Send Email to jimh     
When you buy a pre-made fuel line with primer bulb already in it, the primer seems to be in the middle.

Go new-boat shopping and you'll see practically all factory rigged boats delivered with the primer at the engine end of the line--at least that is my observation.

ibeenfishing posted 03-01-2004 02:13 PM ET (US)     Profile for ibeenfishing  Send Email to ibeenfishing     

I have a brand new "OMC Primer Bulb & Fuel Hose Assembly", the part number is #176268. This is a 3/8" x 10' fuel line.

The primer bulb is about 8 feet from the engine, and the remaining 2 feet would connect to your gas supply. This is with the the arrow on the bulb pointing toward the engine.

I would think these are all made in some automated format. Is it possible the bulb was put in backwards? for a whole production run?

jimh posted 03-02-2004 08:43 AM ET (US)     Profile for jimh  Send Email to jimh     
Actually I didn't mention anything about "ideal" location or say it has to be one way or the other.

I don't think the OMC part is "backwards"--they just make them like that.

Here is what I said in the article:

"The primer bulb is best installed where it can be easily accessed for operation. In most pre-rigged boats being delivered these days, the primer bulb is seen located within 12-18 inches of the engine. This is especially common on boats that have internal fuel tanks. Boats with on-deck fuel tanks may have the primer bulb located at the tank end of the fuel line."

LHG posted 03-02-2004 02:18 PM ET (US)     Profile for LHG    
As a 36 year owner of Whalers powered by Mercury, I can say that the issue (I think this is a correct use of Jim's least favorite word!) being discussed here is possibly brand related. Mercury HAS ALWAYS placed the bulb at the engine end, as far back as my experience goes to 1968, and I believe the earliest Whalers did too. The Nauset/Sakonnet gas tank location under the console almost mandated that the bulb be in the splash well. Mercury's system has worked well for me to this day.

Evidently, OMC does not do this, and I also remember some earlier Tempo lines that had the bulb near the tank, probably in imitation of OMC's procedures.

I know that standard procedure always puts the bulb between the filter and the engine. I would think it makes sense to draw fuel out of the filter, and push it into the engine, rather than the resistance to push fuel through the filter to the engine.

There must be reasons why different brands do things differently, but I have no idea as to what these are. Since primer bulbs have check valves in them, perhaps this is why they are located close to the engine?

phatwhaler posted 03-02-2004 02:39 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
After the great article on primer bulbs I decided it was time to do a little maintenance. I installed a new chrome fuel/water sep (Tempo) to replace the OE Mercury stuff. I also ran new fuel line from the water sep to the engine including a new Tempo bulb. The bulb was installed vertically witht he arrow pointing to the engine. Now the problem:

When tooling along at a low RPM sometimes the engine runs out of fuel? If I proceed to pump the bulb she starts right up again. Incidently, the bulb is not flat or empty when this happens. If I'm moving, say 4000 RPM, the motor runs great and will not run out of fuel.

I have to say that the Tempo brand stuff does not really give me a "warm and fuzzy" feeling. Seems like my grandad used to buy the Tempo pre-made lines that always gave problems. I probably should have bought Quiksilver Mercury parts. My diagnostic gameplan is to take a test tank with me next weekend and bypass the main fuel tank then the water sep etc... Until I pinpoint the problem. But if any of you gurus have any Ideas they would be much appreciated.

BTW, the 24' Justice that was being used by the Coast Guard in Cleartwater, has been regretfully replaced with a Safeboat. Also, there are no more Mercury engines in the fleet either as bothe RHIB and the Safeboat have Hondas. Kinda sad.

phatwhaler out.

ps: I'm not a huge Merc fan but they do have a little more character than Hondas.

LHG posted 03-02-2004 03:06 PM ET (US)     Profile for LHG    
Phat - I had continuing fuel starvation problems with brand new Tempo primer bulbs. I got rid of them, and the problem disappeared. Although I like their gas tanks, fittings, etc, I think their primer bulbs have check valve problems. My Mercury mechanic told me never to use them. Beleive it or not, the Attwood brand primers, about $5 at Walmart, are very good!
phatwhaler posted 03-02-2004 08:05 PM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
LHG, thanks for confirming my suspicions. I think I'll change out the bulb and see what happens.

phat out.

BugsyG posted 03-04-2004 09:11 AM ET (US)     Profile for BugsyG  Send Email to BugsyG     
Hi everyone,

Another fantastic article on fuel lines.

I have purchased a new primer bulb, The hook-ups are correct and the flow is correct. I did not prop the bulb up vertically. However my question for you is, is that when a primer bulb is new, and you hook it up to the engine and pump fuel to it, is there air in the bulb that you have to get out? For instance, I would pump the primer bulb, however it does not get firm at all. No leaks in the engine either.

What I did in the past was, was I took my cowel off, and flicked a little red switch (fuel/manuel start valve), and I would squeeze the bulb and it still wouldn't get firm, however I would close the valve and then the engine would crank over, sputter, then shut down. I would have to repeat the process.

I have also noted that when I would shut the engine down for a short period of time (5-10 minutes), I would have to repeat the process again.

My electric choke in the ignition (the kind where you push the key in to prime it), is broken. I have to take the boat in and get it fixed for spring, but would it constitute for my problems? Thank you for your time.


knothead posted 03-04-2004 12:11 PM ET (US)     Profile for knothead  Send Email to knothead     

I have a 24 gallon Pate Tank with a 90hp Johnson on my Montauk. It was originally rigged with the primer bulb laying flat on top of the fuel tank, about 16" from the access to the tunnel. It would always take several tries to prime and start the motor.

I recently installed a fuel/water filter on the inner starboard side of the splash well, put in new fuel hoses and primer bulb, and installed the primer bulb before the filter, pointing upward, where the fuel line exits the tunnel. The primer bulb works like a champ and when I change the spin-on fuel filter it is very easy to prime the empty filter. I beleive that having the primer bulb in an upright position has more to do with the success of the primer bulb than any other factor, and the most feasible place is where the fuel line exits the tunnel and turns upward towards the motor.

All of this from reading the primer on primers.

Thanks Jim H.


MarkCz posted 06-29-2004 11:21 AM ET (US)     Profile for MarkCz  Send Email to MarkCz     
I think the primer bulb should be installed after the filter since the filter will catch any fuel debris that may screw up the check valves.
Timberry posted 02-12-2006 12:36 PM ET (US)     Profile for Timberry  Send Email to Timberry     

Thanks for your stuff on primer pumps - it is the most useful information I can find by a mile. I drive a diesel. The system has a primer pump on, which keeps collapsing when driving and the engine cuts out, as though it has run out of fuel. It happens every few days and is completely at random. The primer stays collapsed even when the engine has cut out and has been left for a frew hours. This means that fuel is not filling the primer from the tank suggesting a blockage. I've had the fuel lines blown through, changed the primer twice, replaced the filter, changed the tank and sender unit, changed the breather pipe and left the fuel cap off and still the problem persists. I've also looked for a separate check valve in the system but can't find one. The problem definitely suggests a fuel supply problem, but as far as I can see I've done everything I can. Does anyone have any more ideas on what it could be. I'm completely baffled. I'm pretty sure it couldn't be the injector pump because that wouldn't explain hy the primer stays collapsed after the engine cuts out. One other thing - if I let air into the system upstream of the primer so that the primer regains its shape, then close the system again, and prime the pump a few times, the engine runs again! Bizarre! Help!


blacklab posted 02-12-2006 10:37 PM ET (US)     Profile for blacklab  Send Email to blacklab     
Thank you for the interesting and timely article. My primer bulb never seems to get very hard. Someone once told me it should feel like squeezing a superball when primed sufficiently. Mine gets firm, but if you keep steady pressure on it, the bulb will collapse. Is this normal, or should I change the diaphragm routinely. Would a leaking diaphragm cause a loss of power and activate the Yamaha 90 motor "limp home" mode? I have disconnected the fuel supply, and the bulb does get significantly firmer when the fuel has no place to go. Thank you in advance for your answers.


jimh posted 02-13-2006 12:15 AM ET (US)     Profile for jimh  Send Email to jimh     
Re the degree of firmness or hardness in a primer bulb:

I have observed that the primer bulb on my outboard's oil system will get extremely hard--so much so that I thought the bulb had itself become rock hard. It had not, it was the oil filling the bulb.

Also, on hot afternoon last summer my motor's reluctance to start caused me to become rather energetic about squeezing the primer bulb. So much so, in fact, that I precipitated a leak in the fuel system. The leak was actually due to a faulty component, which completely failed shortly afterwards. I believe it is possible to over-prime the fuel system, particularly in motors with carburetors. Extra fuel pressure will lead to the fuel eventually overflowing the carburetor float bowls. Motors with fuel-injection are not quite as easily vented to the atmosphere and will allow more pressure to be accumulated in the fuel supply line.

My boat actually as an electrical priming pump which has a pressure limit. Now I use that exclusively to prime the fuel system to the proper pressure, as it has a check valve which prevents excessive pressure from being created.

Loafer posted 02-13-2006 09:18 AM ET (US)     Profile for Loafer  Send Email to Loafer     
Jim, good stuff and timely too as I’m starting to put my fuel system back together. I had kinda preferred to put the bulb on the tank side between the riser and the bulkhead fitting at the splash well, but I can see the argument for keeping anything at risk of burning or leaking on the water side of the bulkhead. I’d be interested to know what the consensus is on that (CFRs and all notwithstanding).

Timberry, try using one of those hand vacuum pumps at various points to draw fuel through your system. You may be able to blow air back through the line, but if there’s a blockage, say, at the tank screen, then it may be acting like a check valve and (intermittantly) not allowing fuel flow in the desired direction. I’ll bet if you work your way back from the filter, you’ll find the blockage.


nix posted 02-20-2006 07:29 PM ET (US)     Profile for nix  Send Email to nix     
[Gave a long narrative of his engine repairs.]
jimh posted 08-12-2009 06:57 AM ET (US)     Profile for jimh  Send Email to jimh     
Separated several articles seeking diagnostic advice about particular engines and their running problems into their own threads.
Narragansett Outrage posted 08-12-2009 01:04 PM ET (US)     Profile for Narragansett Outrage  Send Email to Narragansett Outrage     
Interesting. I have my bulb set up as described in the article, but I noticed that the local Evinrude dealer has a different set up.

He's got an immaculate mid 80s outrage with a 2006 Etec 225 on it. The bulb appears on the line going up and into the Racor filter, just above where the cables, etc, appear from the conduit and up onto the deck (on the starboard side). So his bulb is actually before the filter, and far before the motor.

Had thought about switching it to his style, but may now just keep it the way it is.

Toffy posted 09-20-2010 02:20 PM ET (US)     Profile for Toffy  Send Email to Toffy     
Hi everybody. No doubt about it, this is a great and learnfull article! I do have one remark and one question.

I found the following sentence at the beginning to be a bit misleading => "This pump (diaphragm fuel pump) has limited capacity to lift fuel from the fuel tank". Make no mistake: as it is a volumetric pump, it is actually the best pump to do this job. It will overcome the suction line resistances without any problem. Even if your suction line is completely dry and your fuel tank is located all the way in your bow.

The real issue with this pump is the fact that it only starts to operate when you crank the engine. This is too late. This means it will take a while [until] you get the proper fuel supply at the carburetors. If it would be possible to start up your fuel pump a bit earlier than cranking, there wouldn't be a problem whatsoever, and your engine would start right away. The time difference problem is exactly what you solve while priming the primer bulb. You fill up the fuel lines and fuel is almost immediately available at the carburetors. If you have an external fuelpump, like me, which you can start before the actual cranking, there is no time difference problem and off course no extra primer bulb is needed.

[Changed topic to discuss fuel pumps and how air passes through them. Please start a new thread in REPAIRS/MODS for this topic. Thank you--jimh.]

Thanks, T.

jimh posted 09-20-2010 06:06 PM ET (US)     Profile for jimh  Send Email to jimh     
A pump is rated in two capacities regarding vertical dimensions: lift and head. Lift is the vertical distance the pump can lift the fuel to its input. Head is the amount of vertical distance which a pump can raise fuel on its output. The fuel lift pumps in most outboard motors are limited in their lift and head. They are also sensitive to restrictions in the vacuum on the input side. I hope this explains the underlying meaning of the adjective "limited" as I applied to the fuel lift pump in my article.

There is no "issue" with a fuel lift pump, real or otherwise. The operation of the pump from engine vacuum is a known limitation of the fuel pump. If you will refer to the article, the introductory paragraph mentions this in its third sentence:

"...[the fuel pump] only begins to function with much efficiency after the engine is running."

I disagree that the pump can overcome any suction resistance in the line. I suspect that pump output volume will decrease if there is too much vacuum in the input line. In the OMC outboards there is a vacuum operated switch which monitors for excessive vacuum in the fuel line at the lift pump input. If vacuum were of no concern, I cannot imagine why a sensor would be provided to warn when the vacuum is too high.

Your question about how air is purged from the fuel system is a good question, but it is not appropriate for appending to his thread. Please start a new discussion on that topic. I will delete that discussion from this thread.

bill705 posted 09-24-2010 01:34 PM ET (US)     Profile for bill705  Send Email to bill705     
I cut an old Atwood primer bulb apart to see what the check valves look like and here are some of the pictures.

There are no check valve springs, just the initial pressure or vacuum when you squeeze the bulb causes them to seat. I don't know if all of the bulbs are like that or not but I suspect that both Mercury and tempo are because you can hear the valves click when you rotate a new bulb.


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