High RPM problems

My engine is running great at idle and rpm's up to 3800. After about 3800, it sputters and will not top out. Tried some carb cleaner in the fuel, ran about a 1/4 tank and now change. Watched the carb and secondaries are copening, not completely, about 90%.
Anybody have a suggestion for my next step?

The carb is a Holley four-barrel.

Slicer Al

Did you recently convert to electronic ignition?

Check timing advance.

No the fuel pressure will not effect all RPM ranges and shows up on high RPM or a heavy fuel demand. At slower speeds the demand isn't as great and thus a lower pressure supplies enough gas. I'm betting that as soon as you back off the gas a little it clears out and runs nornmal.

Did the engine run fine before? all the way through the rpm range? then it started acting up? if so then the timing and ignition system are fine. And someting else is causing your issue.

yes, it's the pump not that it is preventing the bowls from filling up with gas. It's that the pump cannot supply the needed amount of fuel at high speeds.


Did the boat run over 3800 rpm when you first got the boat?   yes or no?

was the conv. kit installed then? yes or no?

Have you changed anything since then? What did you change?


If you answered yes to the first two questions then check the fuel pressure or you can continue to do your dog imitation and run around in circles chasing your ass, I don't care if you keep guessing at it and try ever suggesttion given but at the end of the day there is a process to diagnois (sp) engines and you have to rule out the obvious things first.

Are the first two question yes or No?


The way it sounds is that since you have fuel at the carb and that you can see fuel going down the carb that rules out the fuel pump,... WRONG.

It sounds like someone else that played around with the timing, float level and god knows what else to fix a high idle when they where told the issue was the way they plumb the PCV (breather actually), fixed the plumbing, fixed the idle.

Ok, have you checked the fuel pressure and verified that you have 5 lbs going into the carb? doubt it.

Nick,

I recovered my thread from last year when I experienced this problem. I cut and pasted the outcome. You can type High End Issue in the search box and read my thread.


THREAD FROM 2005:
I received a call from Correct Craft today. The high end issue is one of three things:

1. Electronic ignition wired to ballast.
2. Wrong coil for the electronic ignition.
3. Bad or incorrect aftermarket elect. Ign.

The EI kit that I got from Overton's has a 10 degree something or other and my boat requires a 6 degree something or other. The one I have isn't made by Prestolite which could be an issue. I will know better tomorrow. He believes that I'm only getting 10 volts to the EI not the required 12 volts. NECC will tweak and tune the carburetor too. It only has about 2 hours of use since I bought it.

Ken
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Nautique2001
Senior Member



Joined: June 14 2004
Location: United States
Posts: 398 Posted: June 22 2005 at 12:24am | IP Logged    

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FYI, my electronic ignition kit is made by Sierra. NECC highly advised buying only the Prestolite brand EI. The rotor is completely wrong for this distributor. I will order my parts from Correct Craft now.

My vote is for a fuel pump with a cracked diaphram. Pump still works but not as it should.
Fuel pump rate of delivery is listed in the manual. It was something like 8 oz of fuel in 10 second crank period. Check the manual for this info! Not the same as fuel pressure but also gives a good indication of pump condition.

Nahhh, you covered that already, and it's nothing new on the boat. Not unless the engine is popping and backfiring, but hell that could be a cracked cap!
I agree, you SHOULD see some fuel. Should!!!!
I want to know how in the hell anybody can see fuel in the secondaries @ 3800 rpms! You must be pretty damm close to that carburator, and I certainly hope it isn't being revvvved that high in neutral go figure.
Could be a vacuum leak on the secondary side.... maybe related to that pcv setup.    

I had read in a old motor book for auto repairs that a bad ballast could possibly not deliver enough electricity to the distributer and plugs at a higher rpm . This would rob youre engine of power . For a $5 dollar part it might be worth a try .

my .02

Pat


I can look it up again. If you would like.

I appreciate the help and understand the harrasing, all in fun.

I do not have a pressure gauge at this time and not enough time yesterday to look for one. Did try the volume/time from the fuel pump. Had 8 oz. in ten seconds. Will find a pressure gauge next.

My 2 cents. I had a similar situation last year with a "new edelbrock carb" from a previous owner. I ruled it out and when my pressure tested well I ended up replacing the entire ignition system piece by piece even though I could find nothing wrong with them. in the end it was crud in the float bowls that ended up periodically in the jets that feed the secondaries. It was fun having a whole new ignition system and everything, but since I scrapped it all for the DUI this year it was a bit of a waste.

that's kinda odd, sounds like there is an extra resistor, can you post a picture of it, there seems to be some extra wires for some reason as well.

be carefull most likely the engine will start in gear, they must have by-passed the saftey curcuit completely.

So back to the the main problem, it looks like we still need to double check the fuel pressure first, then we can look inside of the carb for junk floating around. A little trick to flush the jets and metering block if there is dirt or something cloging or restricting the passages is to bring up the RPM and close the top butterfly so that it puts more vaccum on the fuel passages pulling out any crud that may be in there.

Disconnect throttle linkage at the carb, remove the flame arrestor, have the engine warmed up, you don't want to do this on a cold engine. then what you are going to do is open the throttle about 3/4 of the way or so then close the top butterfly with the other hand then release the butterfly and let the engine start to recover then close it again. do this a couple three or four times then let it idle and clear out.

You want to pick-up the rpm and hold it open, not wide open but 3/4 of the way, then as it is coming up on rpm you push the top butterfly close and you'll here the motor load up and the rpm to start dropping, hold it close to the point of it almost dieing then release it and let the rpm come back up, then close it again. Do this severial times if it does die on you then hold open the throttle as you crank it to get it started again.