Hi after 17 months of restoring etc I finally started my ‘73 Scamp with rebuilt engine, carburetor, auto transmission etc. To my surprise it started and runs at idle and when warmed up but won’t accelerate at all. I can gradually increase the RPM’s and it will run but sudden acceleration of any kind and it dies right away. It will restart if I wait a little bit or with a shot of starter fluid. I did put a vacuum gage on the manifold and it bounces rapidly back and forth between 15 – 20 Hg. I can find no vacuum leaks. Any thoughts? Thanks.

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Thanks

Bruce
'73 Ply Scamp 225 1bbl

What carb is on the engine? (Holley 1920?)
Has the valve lash been adjusted correctly?
DD

It is a Holly 1920. No I have not adjusted the valves yet. Would you suggest adjusting them before looking for anything else? Since it does idle how long should I let it run before adjusting the valves?

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Thanks

Bruce
'73 Ply Scamp 225 1bbl

Bruce
You could do a cold lash to get it close or,Run it about 15-20 mins and do Hot lash. I think you will find it helps a lot.
Also saw you post reman carb?? If this is correct and lash is good Carb may be source of problem. Lots of carbs are no good from mass Reman shops.
If carb is bad PM Slant Six Dan he had New ones for sale.
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

With the engine off, remove the air cleaner and with the choke plate all the way open, operate the throttle linkage while peering down the carb. You should see a good, strong shot of gasoline squirt into the centre of the carb throat from the sidewall. If you get only a piddly little dribble, a broken stream, or none at all, there's something the matter with your accelerator pump and the carburetor will need some repair work. Did you rebuild the carburetor yourself, or is this a parts store "remanufactured" unit?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Sounds to me like you have a combination of misadjusted timing and a vacuum leak.

I recommend:

(1) Disconnect and plug the EGR valve vacuum line (If so equipped)

(2) Route the distributor vacuum advance line directly from the carb to the distributor advance pod. Bypass and OSAC valve (if so equipped)

(3) Double check your base timing On a stock 73 motor your idle timing should be at TDC.

(4) Check for timing chain stretch. To do this, rotate the motor by hand until the timing mark is at TDC. Pull the distributor cap. Keeping one eye on the rotor, rotate the engine by hand in a counterclockwise rotation. Stop rotating the motor as soon as the rotor starts to move. Check where the timing mark is at. If the timing mark is beyond 5 degreec BTDC, you need to replace your timing chain.

(5) Adjust your valves with the motor hot. .010 intake and .020 exhaust.

(6) Check your vacuum. A stock motor in good shape with no vacuum leaks should get 17-20 inches of vacuum at idle.

(7) Check if the vacuum advance pod on the distributor is blown and doesn't hold a vacuum. Pop the distributor cap and detach the vacuum advance hose from the carb. Suck on the hose and watch for movement on the distributor pick-up plate. The plate should move counterclockwise and stay there as long as you maintain suction. If the plate doesn't move or moves and then return to its original position then you have a lown diaphragm.

(8) Check your choke pulloff diaphragm. This is another vacuum device that can leak and be hard to notice. Disconnect the vacuum pulloff hose from the back of the diaphragm. Depress the plunger manually and stick your finger over the hole for the hose. The plunger should stay "plunged". It may release a little bit, but that's okay. Just as long as it stays plunged it is okay.

(9) Make sure the plug wires are in the right order in relation to each other and in relation to the rotor. I once bought a Volare that ran, but lacked power. It turned out that the previous owner had done a tune up but had installed the cap 180 degrees off but left the plug wires in the right order. The car ran but the engine was firing 180 dgrees off.

(10) Ditto on the accellerator pump not working. Most likely the rubber gasket around the pump plunger dried up and isn't pushing the fuel anymore. I suggest rebuilding the carb and resetting it all to spec.

Let us know the results.

Adjust the valves first, the rapid fluctuation of the needle on the vacume guage is telling you that there is a Valve that is leaking. More than likely it is because the rocker arm is ajusted to tight that is causing it to leak.


The bog & no rev sounds like the excelerator pump in the reman carb is not working. But get timing & valves set first before you start missing with the carb.


Jess

Thanks everyone for the help. Here is my plan based on the feedback.

First I'll check the carb for a good stream of gas. I did rebuild this carb myself it was pretty straight forward, I took my time and cleaned everything well.

Next I'll adjust the valves and see what happens.

Finally I'll look harder for a vacuum leak or timing problem.

Thanks again I'll let you know what happens.

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Thanks

Bruce
'73 Ply Scamp 225 1bbl

Spray the intake runners and sides of the carb with soapy water and blow compressed air through the PCV hose going to the carb. It should bubble where you have a leak. Especially watch the throttle shaft bushings for leaks.

Ok I've checked for a stream of gas in the carb while moving the throttle and I cannot see any shot of gas. As Dan said this may mean a problem with the accelerator pump. I rebuilt the Holly 1920 myself with a new rebuild kit so what could the problem with the accelerator pump be?

The rebuild was straightforward with one exception and that was with the needle. I could not tell from the re-build instructions or the service manual which way the needle (pointy end) should go. Does the pointy end with the rubber tip rest on the float or point out toward the fuel line?

There are many other suggestions (thanks) for resolving my problem but I thought I would tackle them one at a time so as not to confuse the situation or me.

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Thanks

Bruce
'73 Ply Scamp 225 1bbl

The pointy end of the needle points towards the fuel line (away from carb) You're rebuild instructions should also have shown how to set the float level. This may also be one of your problems if your float is set too low. I think if you had your needle in backwards then the carb would be extremely flooded and probably not run at all.

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You have been getting great advice, but it jumps out at me that if you have a new cam you need to be careful to break it in. I sure wouldn't be doing a long time idling around at 700 or so if my cam was new. If no new cam, you have good advice...set your valves cold, borrow a known good carb and bolt it on and see if your problem is solved. If brand new be sure the water and oil were put in by you to the correct level. Don't rely on someone telling you they did that for you.

rock
'64d100

Don't get distracted. The nonfunctional accelerator pump is the primary cause behind your lack of acceleration.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Hello again,
It is good not to get distracted, otherwise project creep overcomes. I was thinking of acceleration in the pure sense as an increase in rate of change and in particular how fast the engine moved per unit time. It seemed to me the acceleration he was finding lacking was the rpm caused by rotating the throtle linkage so as to increase engine rpm to see how things were working after a build. Particularly since he described a new engine build it didn't seem as if the vehicle was being run on the street, rather that tests were being completed preparatory to a street trial. But I sure understand the urge to take one out without testing awhile first!

I have always found out a lot about a carb on and off the engine by working the carb by hand, and I sure agree that he has a carb problem (most likely) . He still could operate the throttle by hand to achieve say, 2000 rpm and break in his cam by setting the fast idle screw to set there. He didn't say it wouldn't increase rpm, rather as I read it, that if he "jumped on it" the engine speed wouldn't increase as he wished. Upon reflection I do see how he equally as well could have been describing a road trial. Similarly, I see how one could read what I was saying as implying his cam might be the cause of lack of rpm increase and that isn't where I was coming from. Some, if not most of my caution comes from having made the mistakes I sometimes opine upon and my desire was raise a caution only.

Best to all,
rock
'64D100

Thanks again for the comments. I am attacking this one thing at a time so my focus will be the accelerator pump. Dan what could be wrong? How do I repair just the accelerator puump?

As for other comments / questions. The cam is original. This has not been driven yet. I will be ready to drive when I fix the accelerator issue. I am sure at that point I may have other issues but I'll tackle those when they crop up.

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Thanks

Bruce
'73 Ply Scamp 225 1bbl