427/435 tripower hesitation on full throttle

[Clem Z.]

Re: 427/435 tripower hesitation on full throttle

Good idea. I'll get on the Holley web page. I believe I need the tube discharge type.

Thanks,
Ken

any speed shop should be able to order it for you. summit or jegs may even have them in stock.

[Kenneth K.]

Re: 427/435 tripower hesitation on full throttle

I got a .031 nozzle on order and hopefully it will be here next week and I can give it a test. I don't have much confidence that it will completely solve the problem. It seems to me that there should not be a bog with the stock configuration. Changing the nozzle size and other turning tweeks should improve performance.

Ken

[Ken A.]

Re: 427/435 tripower hesitation on full throttle

Ken,
These engines were bad poluters when set up to run right. Since GM built so few cars, they purposely leaned them out to get by with the few state regs that were in place or coming out. The CA cars were notorious dogs and easily blown away by a well set up small block. Even the famous L-88 was pitiful in stock trim at the dragstrip & couldn't last 500 miles at a Nascar track. I saw ZL-1 Camaros run in the high 12's, right off the trailer. Chrysler's Hemi's just flat blew away everything GM & Ford threw at them. Back in our day we lost a lot of Big blocks during our learning curve.
BUT, with a lot of care & tuning AND a ton of new parts from GM to improve reliabilty, by 69 the Big Block began to rule-because you could build one a lot cheaper than a Hemi or a Ford & easily get 600 HP on race gas.
So, hang in there- you'll cure that bog, soon, I hope.
Ken

[Kenneth K.]

Re: 427/435 tripower hesitation on full throttle

Hi Ken/everyone,

I finally received the 0.031 shooter (it's a long story). Anyway, I haven't given up hope. I put the larger nozzle in and tested it last night. The problem is still there, but I do think it might be a little better. I don't seem to have as much of a bog as before, but the hesitation (slow to get the rpms up) is definetly still a problem.

My other observation is the car still runs great when it is cold. I tested it again with the larger nozzle and noted that when the temperature is about 100 F the car runs great. Even at 1/2 throttle the tires will break loose (remember this is an automatic car). As the car gradually warms up the hesitation becomes more noiticeable until it finally reaches operating temperature when the hesitation is the worst.

Could there be anything wrong with the center carb that warps and creates the hesitation when the car reaches operating temperature? Also, I was thinking maybe to put a lower temperature thermostat in? Any other ideas.

Thanks,
Ken

[Ken A.]

Re: 427/435 tripower hesitation on full throttle

Drill it out to an .034. You're now on the right track. When it warms up metals expand and you may get more leaks(air). No problem, just richen up the pump shot & you're done.

[Kenneth K.]

Re: 427/435 tripower hesitation on full throttle

HI Ken,

I found out the thermostat in the car is the 192 F which is one reason the car was running at 200 to 210 at operating temperature. I changed it to a 160 F and it did seem to improve the hesitation a little bit more.

The next step is to find a small drill bit to drill out the shooter to a .034. Seems like none of the hardware stores carry such a small drill bit. I may have to find a place to special order one.

Thanks,
Ken

[Clem Z.]

Re: 427/435 tripower hesitation on full throttle

HI Ken,

I found out the thermostat in the car is the 192 F which is one reason the car was running at 200 to 210 at operating temperature. I changed it to a 160 F and it did seem to improve the hesitation a little bit more.

The next step is to find a small drill bit to drill out the shooter to a .034. Seems like none of the hardware stores carry such a small drill bit. I may have to find a place to special order one.

Thanks,
Ken

you will need to get a holley "holley" squirter screw to get more flow to the squirter. are you sure the ball bearing check valve is working correctly in the pump well ???

[Kenneth K.]

Re: 427/435 tripower hesitation on full throttle

What is a "squirter screw" and what does it do? I assume everything is working fine. I can manually pump the center carb (engine off) and see fuel squirt into the throttle bore.

Can't I increase the amount of fuel to the squirter by using a different colored plastic cam on the accelerator pump? I currently have a red cam on the No. 2 position based on Ken Anderson's recommendation in his power tuning articlein the Restorer.

I found some small wire drill bits so my next step is to drill out the squirter to 0.034. My problem now is the drill bit shank is too small to fit my drill press. I can chuck it in a dremmel tool but I am afraid I will break the bit or get the hole off center if I drill it out by hand. Any ideas on how best to drill this guy out? These bits are the size of a small needle!

Thanks,
Ken

[Clem Z.]

Re: 427/435 tripower hesitation on full throttle

What is a "squirter screw" and what does it do? I assume everything is working fine. I can manually pump the center carb (engine off) and see fuel squirt into the throttle bore.

Can't I increase the amount of fuel to the squirter by using a different colored plastic cam on the accelerator pump? I currently have a red cam on the No. 2 position based on Ken Anderson's recommendation in his power tuning articlein the Restorer.

I found some small wire drill bits so my next step is to drill out the squirter to 0.034. My problem now is the drill bit shank is too small to fit my drill press. I can chuck it in a dremmel tool but I am afraid I will break the bit or get the hole off center if I drill it out by hand. Any ideas on how best to drill this guy out? These bits are the size of a small needle!

Thanks,
Ken

the screw that holds the squirter in the carb body. use a pin vice to hold the drill bit to drill out the squirter. has the throttle arm been repaired on the shaft because i have seen these arms replaced in the wrong position and causing your problem.

[Kenneth K.]

Re: 427/435 tripower hesitation on full throttle

I found an adaptor to chuck the micro bits in my drill press and was able to drill out the squirter. I had to drill it out to 0.035 rather than 0.034 because the micro bits only come in 0.033 or 0.035 sizes.

I didn't notice any real improvement in hesitation with this larger 0.035 size vs the 0.031 size when the engine was at operating temperature. The interesting observation was the performance improved again when the engine is cold. I can't believe how much better this engine runs when it is cold. It seems to be making all kinds of horespower until the car warms up.

When I say cold I mean the temperature is above the 100 F mark on the temperature gage but less than the first hash mark which I think is probably between 160 and 180 F. I am real careful the oil is warmed up a little bit and don't let the rpms increase too high because I am afraid I will slip a rod bearing when it is cold.

In any case, when the temperature reaches the first hash mark on the temperature gage I notice the hesitation returns. If the temperture increase above the first hash mark to say the maximum operating temperature of 200 to 210 F the hesitation gets even more noticeable.

Overall, I think the larger squirter has really helped tune the engine because it runs so much better when it is cold than ever before. The lower thermostat also seems to helps minimize the hesitation by keeping the temperature as low as possible. Maybe this is as good as it will get but I keep thinking the potential of this tripower has not been realized. I woulld think the engine should perform similar when it is warmed up as it does when it is "cold".

Any possibility the temperature issue could be related to an electrical problem as someone has suggested? This car is equipped with the TI and I remember a few years ago I had to replace the engine harness. This harness also has a lead going to the starter, the TI module located under the driver side front fender, and a lead that goes to the coil. After the new harness was installed I noticed a slight performance. Is it possilbe the coil might have a short in it and as the car warms up the coils starts to short out?

Thanks,
Ken

[Michael H.]

Re: 427/435 tripower hesitation on full throttle

I found an adaptor to chuck the micro bits in my drill press and was able to drill out the squirter. I had to drill it out to 0.035 rather than 0.034 because the micro bits only come in 0.033 or 0.035 sizes.

I didn't notice any real improvement in hesitation with this larger 0.035 size vs the 0.031 size when the engine was at operating temperature. The interesting observation was the performance improved again when the engine is cold. I can't believe how much better this engine runs when it is cold. It seems to be making all kinds of horespower until the car warms up.

When I say cold I mean the temperature is above the 100 F mark on the temperature gage but less than the first hash mark which I think is probably between 160 and 180 F. I am real careful the oil is warmed up a little bit and don't let the rpms increase too high because I am afraid I will slip a rod bearing when it is cold.

In any case, when the temperature reaches the first hash mark on the temperature gage I notice the hesitation returns. If the temperture increase above the first hash mark to say the maximum operating temperature of 200 to 210 F the hesitation gets even more noticeable.

Overall, I think the larger squirter has really helped tune the engine because it runs so much better when it is cold than ever before. The lower thermostat also seems to helps minimize the hesitation by keeping the temperature as low as possible. Maybe this is as good as it will get but I keep thinking the potential of this tripower has not been realized. I woulld think the engine should perform similar when it is warmed up as it does when it is "cold".

Any possibility the temperature issue could be related to an electrical problem as someone has suggested? This car is equipped with the TI and I remember a few years ago I had to replace the engine harness. This harness also has a lead going to the starter, the TI module located under the driver side front fender, and a lead that goes to the coil. After the new harness was installed I noticed a slight performance. Is it possilbe the coil might have a short in it and as the car warms up the coils starts to short out?

Thanks,
Ken

Not sure what the actual problem is on this one but one thing is for sure. It shouldn't be necessary to make changes to original carburetor specs to correct the problem.
These cars didn't have this problem when new so there's no reason why several items/dimensions/settings in the carburetor would have to be a lot different than original to run properly today.
The "fixes" so far are just an attempt to cover the real problem somewhere else.

[Duke W.]

Re: 427/435 tripower hesitation on full throttle

I couldn't have said it better myself! Time and time again guys resort to backyard engineering to "fix" problems rather than finding the root cause and correcting it.

In this case I believe the basic problem is an aftermarket cam with too much overlap based on the idle vacuum readings that were stated in the first post.

Duke

[Clem Z.]

Re: 427/435 tripower hesitation on full throttle

Not sure what the actual problem is on this one but one thing is for sure. It shouldn't be necessary to make changes to original carburetor specs to correct the problem.
These cars didn't have this problem when new so there's no reason why several items/dimensions/settings in the carburetor would have to be a lot different than original to run properly today.
The "fixes" so far are just an attempt to cover the real problem somewhere else.

back in the 60s i tuned a lots of 3 X 2 corvettes and i never had to change the pump shooter to get rid of any bogging problem. i still think you have another problem. i would try heavier springs in the end carb vacuum diaphragms to make sure they are not trying to open to soon.

[Kenneth K.]

Re: 427/435 tripower hesitation on full throttle

It's not the springs as I disconnected the end carbs so they could not engage and the hesitation still occurs. This test isolated the problem to the center carb. I still think the key is the temperature. Why does the car perform so well (idle, throttle, etc.) when the temperature is relatively low but hesitates when the temperature increases. The more the temperature increases the more the hesitation becomes. Note also that before I put the tripower on I tuned the car with a 4 bbl and it ran great... no hesitation hot or cold. If the cam was not to OEM specs why would it run okay with the 4 bbl but not the 2 bbl center carb?

Ken

[Timothy B.]

Re: 427/435 tripower hesitation on full throttle

Ken,

I still think there is a internal vacuum leak caused by throttle shaft wear or throttle plate sealing which is confirmed by the fact you say the engine will idle with the idle speed adjustment screw backed all the way out. This could be in any one of the carbs but the center carburetor is the most used.

Is there a throttle plate adjustment stop screw on the end carburetors. If so, check to make sure the plates are closed and the screw just touches the lever thus keeping the plates from sticking when closed.

The engine vacuum is not pulling fuel from where it's supposed to, thus hesitation.