cdaniel525

iTrader: (1)

Just installed a new motor in my 24' Sunsation... and had to pull the intake manifold and replace a set of lifters due to one of them being bad and knocking.... Prior to that the motor seemed to idle and be great under throttle (though only went for a quick 15 minute ride till I found the knock).... Threw it all back together, and while in neutral, if I rev the motor up to 2500 or 3000.... and then if I rev it some more it will hesitate momentarily and then rev up.
Took it for a ride and then it doesn't hesitate under throttle... It actually runs killer and accelerates great.
However it does hesitate, kinda almost like bog like a car would... when coming off a dead idle (when in gear).
I dont think its something with the timing, BC I tried adjusting timing from 8-12 btdc at idle... and 32-36 at 3000... and still same result.

Is this probably a bad power valve or something else I should be looking at??

TIA - Chris

GLENAMY 242SS

iTrader: (1)

In a car or my bike I would look at accelerator pump.

mike tkach

iTrader: (3)

sounds like acc pump or incorrect power valve.did you put a vacuum gauge on it and check how much vacuum it has at idle.if you have 12 inches of vacuum you need a 6.0 power valve.whatever your idle vacuum is half of that is a good starting point for the power valve.maybe mild thunder will chime in,he is a master at tuneing carbs.

SB

iTrader: (1)

I can't tell you how many times I've seen carbs where the accelerator pump linkage is not touching the accelerator pump arm, after someone has taken apart a carb.

ie: the arm from the floatbowl is pointed up, and the linkage (w acc pump spring) is not setting on that arm.

edit in: double pumpers - and thus why named so, have two of these. One in front, and one in rear of carb.

Easy to do if you don't know to look for it when re assembling.

MILD THUNDER

iTrader: (3)

What kind of carb is this? Holley, quadrajet, etc?

Typically sounds like an accelerator pump issue. But, if you're "easing" up on the throttle and it falls on its face, or sneezes back thru the intake, it could be a lean condition as well. I'd also make sure you don't have a vacuum leak since you just had the intake off too.

cdaniel525

iTrader: (1)

Thanks for the all the replies guys....

This is a Demon Carb... I think a speed demon. After reading your posts, I went and checked out the accelerator pump... and it was connected properly as SB suggested to double check. Actually I found that the adjustment screw was pressing down on it while at idle. Where as the secondary acc. pump had no tension and could be slightly jiggled around, which I believe is the correct adjustment?

I backed the primary acc. pump adjustment screw 1 full turn back, but it still seemed to be putting some slight tension on the arm... After that I ran it and still seemed to have that hesitation! Also worth mentioning, that it still does the same thing at 2500-3000RPM, only when in neutral.

I guess I really need to back that screw off till its just got some slack in it... is that correct!? Do you guys think that its dumping too much fuel too quick?? I wonder why I didnt notice this problem when I first took the boat out... maybe I need to check the intake for leaks, but I silicon'd the **** out of the front and back of it...

Im also going to hook up a vacuum gauge and make sure power valve is correct... Tho from what you guys are saying and a Holley video I watched, doesnt seem like it would be the issue?

Drew555

Check the float level. I just had to readjust mine. My thought is we are getting more than 10% ethanol these days and it's less dense causing it to dump fuel into the carbs. Just went through this last weekend. Take the flame arrester off after running and see if it is dumping into carb.

GLENAMY 242SS

iTrader: (1)

What is the cfm? What motor? Specs of motor?
Maybe too large of a carb? Wrong squinters? Are you running 30 or 50 accelerator pumps?

MILD THUNDER

iTrader: (3)

Did you check to see if when advancing the throttle lever, you are getting a good squirt of fuel from the squirters in the carb?? Adjustment is one thing, a bad accelerator pump diaphram, clogged orifice to the squirters, or clogged squirter, can be a whole separate thing.

Siliconing the front and back of the intake doesn't really have anything to do with a vacuum leak.

When you had this intake manifold off, to replace the lifters, what was your procedure for adjusting the valves after replacing the lifters?

cdaniel525

iTrader: (1)

850cfm, BBC Mark IV - 489 Stroker, 9.0:1cr,
Intake Duration at 050 inch Lift: 236
Exhaust Duration at 050 inch Lift: 244
Intake Valve Lift .588
Exhaust Valve Lift .595
Lobe Separation (degrees):114

I was thinking about maybe trying larger squirters after watching a Holley video saying too small of squirters can cause a lean condition and bog the motor.... Not sure what size the acc pumps are though...


Forgot to mention that I did have a good deal of gas when pressing on the lever...
To adjust the valves, I took the longer more painful method, but knew itd be good... I watched the cam through the block, and waited till the lifter was on the flat part of the lobe, then tightened the nut till the pushrod had just a bit of tension, then gave it an additional 3/4 of a turn.

Where should I be looking for a vacuum leak then??

Thanks again.... Chris