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View Full Version : Bogs/dies on Holeshot, no other symtpoms


Hoff1
08-04-2005, 09:56 AM
Guys, need some expertise. Got a 1990 351 with 4160 carb. Problem is that when I try and hammer it out of the hole, then engine will bog down and die. If I left the rpmís get above about 1200, I can give it all its got. Itís only on the holeshot that it seems to have problems. Doesnít seem to be running too rich at idle. My top end is aroudn 4200 rpmís and there are no symptoms after the start. I tried adjusting the fuel/air on the carb. It doesnít seem to get any better with adjusting the fuel/air or the idle. It evens starts to backfire if I try too hard.

I got a new power valve recently installed. Plugs got less than 20 hours on them. This could be a lot things, but Iím trying to narrow down my list. Boat is 2 hours away, so maintenance is not easy. Could the points/condenser be causing this (I know I should have changed this out with EI years ago)? I'm going back down tomorrow and don't have time to order a EI conversion kit. These symptoms have only showed up in the last couple of weeks. Was running like a champ before then. TIA for any advice.

6ballsisall
08-04-2005, 10:05 AM
If you have gone thru the carb as mentioned I'd be checking your points/ replacing them (they are cheap anyway) Also, how is your fuel pump? How about your fuel filter?

Hoff1
08-04-2005, 10:37 AM
I donít have a clue on checking the fuel pump, howís this done? The fuel filter is 2 seasons old. What are the symptoms of a bad points? These are probably way past due for some kind of maintenance/replacement/converting.

87MC Dave
08-04-2005, 11:59 AM
If you are backfiring then you are not getting the proper spark to a/all cylinders. I would certainly check my points to make sure they are not worn out and order the conversion kit and get it installed....Really easy to do...just make sure you hang on to your old advance springs for the distributor just in case. I had a problem with that...but back to the other...could be a plug going bad, I had one go bad with only a few hours on it...just some things to check...

Bruce Carr
08-04-2005, 12:44 PM
Couple of things to look at:

Is your accelerator pump shooting a good stream of fuel into each primary when you open the throttle rapidly? To check, hold the choke plate open and look down the primaries while you manually open the throttle in a fairly rapid movement. You should see a stream of fuel shoot out into each barrel. If there is no stream of fuel, your accelerator pump diaphram is probably bad. Lack of adequate enrichment when you drop the hammer will certainly cause the bog you describe.

You mentioned a new power valve was installed. It it the proper size for your application. The power valve enrichens the primary circuit when the engine is under load. The power valve is operated by a drop in vacuum when the throttle is opened and the engine is loaded up. The incorrect size valve can either add to much or too little fuel into the circuit which can cause bogging.

Hoff1
08-04-2005, 01:21 PM
I thought about a bad plug, but I would expect the engine to have uneven idle. Iíve left a plug cable unhooked and started the boat before. Shakes the bejesus out of the thing. Boat idles fine, after the initial take off everything seems normal

Bruce, Iíll check the accelerator pump as you describe. The power valve is a 6.5, which is the same size Iíve been using for a couple of years. The first time I used the boat after I replaced the power valve, it ran like a champ. But, it started having problems yesterday.

I think I might take a look at the points as well. Is there a ďhow toĒ explanation on the points somewhere. Iíve been trying to find one, but have been unsuccessful. It seems all I can find is EI conversion, which is fine for 1-2 weeks from now but wonít help me out tomorrow. This seems like something that might get me moving quicker than waiting for a EI conversion kit from skidim. Thanks for all the help guys, any more ideas.

87MC Dave
08-04-2005, 04:43 PM
Had the same thing happen...Boat would idle fine...I could even rev it up...while in neutral...But when I put it under load it would spit and sputter back fire and carry on....changed the plugs and she was fine. It ran fine the day before, but that morning it started acting up. I have no explaination for it. I changed the plugs and the problem went away.

Hoff1
08-04-2005, 05:34 PM
Now that you mention it, I think I started have some of these issues at the end of last season. I changed my plugs and problems seemed to go away, even though the old plugs looked virtually brand new when I pulled them out. This might have led to my power valve getting blown due to backfire.

I think I've narrowed it down to either fuel or ignition, which means there are only 263 possibilities left to evaluate, or should I say 351 possibilities. Gotta love engines.

I think my first steps will be to check the accelerator pump and the points. Excuse the dumbness of myself, how do you know if you points are bad? Will they look corroded, or black, or something? Iíve never actually opened up the distributor, so Iím learning off of pictures only.

87MC Dave
08-04-2005, 05:44 PM
The cheapest and fastest thing to change is the plugs. it won't hurt to change them and it is alot cheaper than tearing into carb. and if it doesn't fix the problem then you haven't really lost a whole lot of time of money...

redmike
08-04-2005, 09:17 PM
Hoff, the point contacts should be even, and not look burned/black. One other thing you might look at is if the vacuum advance on the distributor is working. An easy way to do this is remove the vacuum line from where it goes into the carb, plug that port, start the motor, and suck on the vacuum line. The motor rpm should increase, if it doesn't, it won't advance the timing when you first hit it.
All that said, I would look at the accelorator pump first. It is an easy changeout, discussed before.

Hoff1
08-08-2005, 07:48 AM
Thanks for the help on this guys. I did some investigation on Saturday and it looks like the accelerator pump is not squirting any fuel as Bruce had mentioned. Looks like itís time for carb rebuild. Iíve never attempted this, but my gearhead brother was some experience in engines.

Other than this little issue, the boat ran great all weekend. With a little care on the holeshot, didnít have any stalling issues while I was boarding.

Hoff1
08-08-2005, 11:00 AM
Wanted to give an update from what Iíve been able to research through pictures on the internet. Apparently, when I replaced the power valve recently, upon reassembly I failed to place the accelerator pump lever back in the correct position under the adjustment screw - oops.

I happened to notice that this lever was not doing anything yesterday and was free floating, but was unsure of its purpose. Appears it was an oversight by an under experienced carb mechanic (myself). Always wondered what the thing did, guess I know now.