Do I need the primer pump?

[kdc2000]

I have a 1987 35 hp Johnson and have been tracking down cause of problem of stalling and hesitation when transitioning from idle to medium rpm.<br /><br />I replaced all fuel lines. Found some suspect leaks and this improved the problem.<br /><br />I rebuilt fuel pump. Still a bit better.<br /><br />Rebuilt carb. Better yet but still the problem is there.<br /><br />My question is, can I bypass the primer pump mounted to the front of the motor by running the fuel lines that go from the carb. to the primer pump directly to the intake manifold instead and just use the primer bulb on the fuel line? Or, could I just plug the hoses that run into and out of the primer pump? I'd like to remove any possible impediments to the gas flow.

 

[petryshyn]

Re: Do I need the primer pump?

I am puzzled that you have 2 primer bulbs...Was this an add-on?<br />If the engine performs fine at wide open throttle, it is unlikely that you have a fuel flow problem. To prove this, simply keep the primer bulb firm while accelerating to see if the problem persists. If the problem is resolved with a firm bulb, then suspect fuel flow and/or pressure.<br /> Idle mixture adjustment is crutial for proper low speed to high speed transition. Try adjusting the idle mixture out a 1/4 at a time to richen mixture. Lean idle mixture often causes hesitation...<br />Also be sure you have strong ignition, and check for proper timing....

 

[Yepblaze]

Re: Do I need the primer pump?

I think perhaps, he might be reffering to the enrichining(choke/primer) system?<br /><br />A stumbble or lean condition on acceleration could still be, compression, (do a decarb), ignition (weak or improper adjustment), low float level (check it against the recomended setting), poor fuel delivery, (usally shown when pumping the bulb during the condition)<br /><br />or maybe a physical little plugging of one of the carb jets you missed, (shown by correction of condition if choke is temporarily left partially on, or a squirt from a bottle of premix, if it doesn't have a choke).)

 

[kdc2000]

Re: Do I need the primer pump?

Thanks for your help. To respond to your questions.<br /><br />Schematic,<br /><br />I have a primer pump (I refer to it as a pump instead of bulb because it has a plunger instead of air bulb) mounted on the front of the motor. It injects fuel from the bowl into the manifold and throat of carb when pumped. The primer bulb I mentioned is the one on the fuel hose from the tank to the carb.<br /><br />Yepblaze,<br /><br />The compression is good, I know the float level is correct and neither primer pump or bulb improve the condition.<br /><br />Both,<br /><br />The problem doesn't seem affected when I pump the bulb on the primer 'tween the tank and carb (it stays firm) and the primer pump on front of motor doesn't seem to have any fuel pressure feeling of resistance when I pump it after the motors been running for a couple of minutes (this is why it's got my attention) so it doesn't improve the hesitation/stalling.<br /><br />Schematic, Yepblaze or any others,<br /><br />Plugs are new but my wires are a little suspect. Other than wires what are the most likely culprits in my CD Ignition System.

 

[Yepblaze]

Re: Do I need the primer pump?

So if stabbing that little enrichener while it is doggy doesn't help, maybe it's just over propped, or the ignition is not advanceing correctly.

 

[kdc2000]

Re: Do I need the primer pump?

Is there some kind of CD Ignition system tune up kit?

 

[kdc2000]

Re: Do I need the primer pump?

Yepblaze,<br /><br />After searching through my service manual for spark advance issues I found the procedure to syncronize the throttle/spark advance. I found this was set WAY off. I'm surprised the thing even ran. I've got it dialed in now. Thanks so much for your help.