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engine question

nebraskaairboater

nebraskaairboater

Well-known member
I have a 500 caddy on my boat direct drive. it runs great turns the 74" sensenich q blade at 2700 rpm on about 2.5 setting. When I am running at around 2000 and push the throttle to WOT it hesitates (rpm falls) then turns back up to 2700. Is that most likely the timing or could it be something else. I timed it by ear. most rpm at wot with it still shutting off and starting. I have the vac advance hooked up to the carb but nothing else vacuum wise. The carb is a 600 Edlbrock with vac secondaries. Any advice appreciated.

Thanks,

Dan
 
NebraskaAirboater,

Cool pictures! Looks like ya'll got some beautiful country our there. Can you run for hours without seeing people?

I don't know of many people down here yet that are still runnin their vacum advance. Most, (including my boat and most performance engines) are only running mechanical advance.

You might want to PM Waterthunder! This man has an infinate knowledge of the GM car motors and the correct way to tweak them!

Also sounds like it could maybe be the power valve or the accelerator pump in the carb?

Basketcase
 
That's definitely a fuel problem. Sounds like your accelerator pump isn't working.
 
well I would try using a timing light and if you ask thunde rhe can tell you what the total timing should be. I would disconnect the vacum advance and let the distributor advance mechanically I believe they all will do it.

But most importantly thunder is the one I woiuld listen too if you can get him to tell you and he seems pretty good about sharing info with folks.
 
IF you are not having problems from idle to 2000 with hesitation it is most likely not the accelarator pump. You should check the vacuum secondaries. They are opening too fast causing a lean spot. When the fuel catches up with the air it goes ok.
Tim
 
we need a response from thunder, where art thou ??
and please pm me with the part #'s, thanx thunder
 
the only peple you see are other airboater, and river rats out playing on the river. You can ride for hours in each direction from Fremont. It is nice. I was trying to get some pictures of sand hill cranes that are all over out here but they would sit still until I got the camera ready then they would fly on to the next place.
 
A Carter uses a weighted butterfly and vacuum to opening the secondaries they don’t have a power valve. A Carter is a lot more tunable then a Holley. But I prefer a Holley they will always make more power. However the first thing I would do is disconnect the vacuum advance from the distributor and install a curve kit in you distributor their less than $15 and run the weakest springs in the kit. Then set your total time with a timing light. Set your total timing with your motor at the max rpm you can run your direct drive. See with a direct drive your motor never reaches enough RPM for the stock ignition system to fully curve out so you never have enough timing in the motor. After you do this then start playing with the carb. I would first try a larger discharge nozzle and possibly increasing your plenum velocity. What intake are you running?
 
AutoZone and Discount sell the curve kit's, MrGasket PN#720-929G for a H.E.I. or if you have points kit #720-928G Their $10 in Jeg's. Let me know how this help's and we can go from there.
 
i'm running the stock iron intake this year but next year I plan to run the edlbrock aluminum one. I put a light on it the other day and the mark is at about 12:00. a long way from the indicator gauges. When I time it down to where it even shows on the gauge it runs real slow and don't have as many rpm's as it does now. (Balancer slip?) If I advance it more than it is it starts real hard after it warms up. I converted it from points to the HEI type distributer when I put it on my boat.
 
speeking of the timing chain, just disassembled my 500, pulled the oil pan off....and trick or treat, half of the lower timing chain pulley, and a few teeth...seems the previous owner replaced the chain and shattered gear and never bothered looking for the missing pieces....amazing
 
T-REX - Man that is almost unbelievable, almost. Somebody was mighty lazy or stupid. Glad none of those parts went somewhere that could cause problems.
 
T-Rex,

I found that in a 454 Corvette once. It belonged to a neuro-surgeon, no lie!!

Jim
 
454 vette, that sounds like fun !!
and im not not sure if lazey is the correct word, but definitly
not having good intentions. i think i counted 10 half inch bolts on the oil pan, maybe 25 mins worth of work to r and r the pan. thats pathetic to think of the possible consequences.
thats where if thunder was inspecting a motor the seller would shit himself.
that oil filter would have to be full of metal of some sorts.
also this same motor had 2 bent pushrods and 2 lifters with big (1/8 inch pieces of metal broken off the top edges (rim) .
 
It's an old motor... 1974 - 76. As far as I know it is all stock. I was worried about the timing chain as well but am hoping to get thru the season without changing it. I do plan to do it this winter just so I don't have to worry about it. This week I will be changing the rear seal and oil pan gasket to try to curb my oil leak. I'll let you know how that goes. I don't plan to take the engine off my boat to do it.

Thanks,

Dan
 
It does sound like your balance ring may have slipped. The best way to check with out pulling off the heads is by a TDC whistle. If your not worried about getting it exact you know just want to check it. Pull out #1 plug and turn the motor by hand while holding a long thin screw driver in the spark plug hole. Try to locate the end of the screw driver in the center of the bore on top of the piston. Do this slowly and carefully making sure not to put the screw driver into a bind. Watch the screwdriver move as the piston pushes it up exactly when the screwdriver stops moving you are @ TDC on number one. Then look at your timing marks if there off you slipped you hub and your timing marks are irrelevant.
 
T-Rex,

The 454 Vette was fun when I got it right. The oil pump intake screen area was full of plastic teeth.

I spent a lot of time on the engine, steering, and suspension. The kid that bought it from me said it drove better than a new one. The car was over 10 years old then. The big block Vettes had a bad handling reputation that they did not deserve. It was fixable.

Jim
 
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