No Power Under Load

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Chuck Watson
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No Power Under Load

#1 Post by Chuck Watson » Tue Mar 08, 2016 5:56 pm

I have a fairly new-to-me vintage racer. I have a persistent problem that neither I nor my local p-car shop has solved. Essentially it runs great and revs great in neutral, bund under load it is weak. Here is what I have done:

Carbs: checked out my Solex's for proper jetting, float levels. Adjusted accelerator volumes. Synchronized them. Made sure they perform as expected from a bench perspective.

Ignition: replaced dizzy cap, wires, plugs (regapped), rotor and replaced the old electronic distributor insert with an newer Ignitor unit. New battery. Set timing.

Fuel: made sure adequate flow, replaced pressure regulator, confirmed filter not plugged.

Engine: adjusted valves

What am I missing? This is putting me over the edge! :shock:

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Jeffrey Leeds
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Re: No Power Under Load

#2 Post by Jeffrey Leeds » Tue Mar 08, 2016 6:04 pm

Do you mean the car doesn't move? Or it doesn't accelerate with any force? Or?
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Chuck Watson
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Re: No Power Under Load

#3 Post by Chuck Watson » Tue Mar 08, 2016 6:11 pm

It runs but it is down on power. We had it on the dyno and I don't recall the HP, but it was very low. AF ratio was fine however. Seems to point more to ignition than fuel system.

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Jacques Lefriant
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Re: No Power Under Load

#4 Post by Jacques Lefriant » Tue Mar 08, 2016 6:49 pm

Did the engine ever make power?
 

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Pascal Zundel
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Re: No Power Under Load

#5 Post by Pascal Zundel » Tue Mar 08, 2016 6:56 pm

Have you measured compressions?

Chuck Watson
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Re: No Power Under Load

#6 Post by Chuck Watson » Tue Mar 08, 2016 7:21 pm

Pascal -

Compression will be next on my list. I was hoping the ignition component replacements would do the trick, but no. I have to grab a helper to do the compression readings.

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Re: No Power Under Load

#7 Post by David Jones » Tue Mar 08, 2016 7:40 pm

Where are you? When you say vintage race car, is it a race car or track day car or just a 356 prepared for fast street use? . Who built the engine and to what specs? The engine builder should know what HP to expect and where it should make it. If he does not then he should not be building "race" engines. What is the max ignition timing supposed to be? It should be at least 34 degrees BTDC above 3K rpm. Don't bother with a compression test do a leak down test. That will tell you far more. There could be a myriad of reasons why it produces less power than you expect. Take it to a mechanic who knows these engines and he should be able to get a fair idea of why it is down on power. For a present day vintage racer I would think 150 plus hp would be the norm.
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Adam Cultraro
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Re: No Power Under Load

#8 Post by Adam Cultraro » Wed Mar 09, 2016 12:01 am

Down on power is pretty vague really. You need to do two things - a leakdown test and a compression test. If I could only do one, I would do to a leakdown test. For a motor not making any power, I would want to ensure that first and foremost it is airtight - meaning no worn rings, no burned valves, no worn valve guides, etc.

A leakdown test will instantly tell you the condition of the valvetrain and rings, basically everything that keeps the motor airtight. Any loss of performance here results in lost compression, which is probably what you are feeling.

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Re: No Power Under Load

#9 Post by Martin Benade » Wed Mar 09, 2016 8:21 am

The one ignition part not mentioned is the coil. Have you tried swapping it too? By down on power do you mean 60hp instead of 90, or so little power it can barely be moved?

Chuck Watson
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Re: No Power Under Load

#10 Post by Chuck Watson » Wed Mar 09, 2016 10:19 am

Here is a little more detail for those who asked. Yes, it is a fully-committed racer. Not street legal which makes road testing difficult. It was built by an experienced P-racer in the RMVR group 20 years ago. I am in touch with him and he has been great, but the car went through several owners before I got it and the paperwork was mostly lost. So I have to uncover the facts as I go. Here is what I know:

Engine machine work by Walt Watson. Other components by Skirmants.
Scat Crank
High Compression with Big Bore kit. Around 11:1
Runs 110 Octane
Norris 356S cam
Rev no problem up to 7K
Timing is around 33 or 34 currently.
Lightened flywheel
Heads cleaned up.
Bosch 009 Dizzy
NGK B7S plugs - new
Compomotive wires - new
Holley Blue fuel pump
Fuel pressure regulated a 4 psi
Total Fail charging system (i.e. no alternator) with new Yellow Optima
Yes, I did replace the coil (which was my first guess)

The car pulls like a freight train up through about 4000-4500 rpm. Then it plateaus or even drops off a bit. Seems more ignition related than fuel. But I will do a compression test since I have the tool. If that looks weak then I'll get a leak-down test done. Other than a compression issue I can only guess it might be a sloppy dizzy or maybe a fuel stoppage somewhere I haven't found yet.

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Vic Skirmants
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Re: No Power Under Load

#11 Post by Vic Skirmants » Wed Mar 09, 2016 11:03 am

Carbs? venturiis? main jets? Float level, and finally size of the needle valve.
When you say Big-bore; 86mm? Not legal for what we run.
83.5mm and 165 HP.

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Re: No Power Under Load

#12 Post by Chuck Watson » Wed Mar 09, 2016 3:01 pm

Vic -

I am running Solex 40PII-4's. Currently with 35mm venturis. They were jetted with 170 mains which showed up rich in an earlier dyno run and were subsequently reduced to 160's which gave a good AFR. I am at about 800' above sea level. Air Corrector jets are 160. I have set the float to slightly below the stock spec line per my understanding of differences with today's gasoline. Accel pump is just a dribble. I believe the needle valves are 1.75. They are the spring-loaded type. Most items adjusted to Duane Spencer's book by original builder and confirmed by me. I have your velocity stacks. I was told it had a "big bore" kit but have not confirmed size.

I have not confirmed the "flatness" of the bottom flanges of the Solex's yet, so perhaps that is another avenue....

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Jan Balder
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Re: No Power Under Load

#13 Post by Jan Balder » Wed Mar 09, 2016 5:53 pm

Have you reversed #3 and # 4, or, # 1 and # 2 plug wires ? :shock:
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Jacques Lefriant
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Re: No Power Under Load

#14 Post by Jacques Lefriant » Wed Mar 09, 2016 7:31 pm

CJ must have installed a stock "C" camshaft while no one was looking.
 

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Vic Skirmants
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Re: No Power Under Load

#15 Post by Vic Skirmants » Wed Mar 09, 2016 11:24 pm

Chuck, carbs sound good. 170 mains were certainly way too big.
Jacques asked if it ever made power; did it? Or it never has performed as expected?

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