The Stovebolt Site Forums The Shop Area Engine Shop Bad Hesitation

I have been chasing my tail on this hesitation, it occurs between about 1000-2000 rpm. When I accelerate from a stop it feels like the motor is not getting any gas but as I back off the throttle it picks up. Once it is over that rpm range the engine accelerates fine. I have tried more advance and less advance on the ignition with no luck it gets worse either way although it seems better with less. I opened up the carb and cleaned the jet and the needle next to it, checked the float and gaskets. It idles smooth and revs in neutral OK but if you rev it quickly it stumbles a bit. The accelerator pump works but it seems like it is a fuel delivery problem, is there any tuning or adjustment to the accelerator pump? I didn’t see any

I once had a bare spot on the wire from coil (-) to the points. Every time the vacuum advance moved, the engine cut out as if it had no fuel.
Some thing to check.
If you think it is losing fuel, try choking it a little and see if it improves. If so, definitly fuel.

Steve,

What carburetor you got on that motor? If it is a Carter, the accel pump is not directly linked to the linkage, but rather it is connected via a spring. If you stomp on it, it takes its sweet time to pump fuel into the motor, meanwhile the butterfly is wide open and you get a lean mix.

Does this happen only during accel or does it happen whenever you are in that rpm range?

Try the artificial enrichment method of carb adjustment.
.
Does your vacuum advance unit have a pin-hole leak?
.
What is the dwell on the points?

OK here we go,

Curly thanks, it's not a wire shorting.

Ken, I have a Rochester and it seems to be in that rpm range not just when accelerating.

Luke, I thought about dwell after I posted this and I don't have a dwell meter here, what is the dwell spec. I will check the vacuum advance also but it stays put when it moves. I have tried the choke that is no help it's still stumbles.

That and the engine is way down on power at this rpm range, going 20-25 MPH in 3rd it just bucks when throtled on flat ground. I live in a hilly area and going up my street it is poping and hissing at first then it passes that speed range but it lacks power to shift into 4th. It could well be the dwell I have not checked it with a meter but I did look at the points yesterday and saw daylight between them. What is the airgap on the points and I will check the setting.

As I recall the points gap on the 206 is 0.18.

Dwell around 32 - 34 deg. is ok .
Sounds like a carb problem . Did you do a full strip down and clear all the passages and jets ?
Sometimes it doesn't take a very large piece of grit to foul a passage , but blowing back through every drilling , with all the jets and metering devices removed can work wonders .

HHmm interesting. I have the same sort of problem with my 250. HEI, 'New' carb..Still has a stumble and fart about 1800 rpm when I put my foot into it and the auto box is in third. (no kickdown cable) Sometimes it happens when cold in the other gears. It was stumbling and fart real bad, but that was a cracked rubber vacuum plug. Fixing that helped alot, but there still is the intermittent stumble.

Steve,what model Rochester are you running on that old truck? Your description seems to be lean carburation

Here is the latest,

I started the truck this morning to go to work and had RTB back home within a mile.

Thanks for the dwell info I will check it tonight.

Tony and Dusty, I am righ there with you on this being a lean condition. I am going to put an electric fuel pump on tonight and see if that cures the problem.

Dusty, I had the carb off and down twice I did not have wire drills with me so I guess I will try again. Do you have any comments on drilling the power valve passage.

Tony, I don't know what part number it is but it has a 51 main jet. I looked at the Rochester hop up page on the Inliner site and used that as a guide for mod's, I have not done any yet

The funny thing is I tried using the choke to fatten it up and it ran worse.

Steve,I assume you have a model B carb, generally the main jet has little effect on part throttle drivability unless the jet is really plugged up.Is your intake manifold heated by the exhaust and does it work properly? A Rochester B on a cold intake manifold is hesitation prone.The power valve is normally in the enriched position,until engine vacuum closes it,the little piston moves freely?The small tight wound spring is present?
Also look down the carb throat, there is a round spray bar running across the diameter. The middle of the bar has one or two small air bleed holes in the top. take a strand of stranded wire, like from 16 guage and push on end into one of the holes. This will richen the part throttle response. See if runs better or worse.Sounds like you have cleaned the carb well, no possibility of crud in that spray bar?
Of course your problem may not be the carb so....

This 'B' carb is on the 207 ,, right ? ,, so the main jet is ample big enough , a 50 would be more economical .
Drilling in the carb ,, NO WAY ! maybe push a little fuse wire thru the passages and wee holes , nothing violent though. Compressed air and carb cleaner solution is my preferred tools . These are metered holes , carefully designed , and dont take well to tinkering , end result gross fuel consumption . Does the condition clear as the engine warms up ? Is the heat riser box working ?
You have checked the carb to manifold gasket , and the manifold to cyl head ?
As Tony says " The power valve is normally in the enriched position,until engine vacuum closes it,the little piston moves freely?The small tight wound spring is present?"
You say it accelerates fine over 2000 rpm , , an electric fuel pump will not change that .
This is a part throttle problem , which means an emulsifier tube or power valve problem ,,
or something completely different (like the vaccuum advance) but I don't think so .

OK I have checked the spray bar and tried a restriction in one hole, no real change. I drove the truck around the block it hardly made it. I am now wondering about the coil, I changed the charging system to 12 volt and I never put a balast resistor on the coil. I have an MSD coil on my SEC but it has an HEI terminal on it. The truck starts fine and idles well, I'm thinking the coil is breaking down and the increase in pressure is causing the problem?

I have to say at this point it has become worse and will not rev above the hesitation range. I put some fresh gas in and that did not help any either. I am going to pull the plug right now

Pull the plug , eh , , , I guess that means you're ready to send the truck over here then
OK , I just re read the post properly ,, you say pulling the choke only makes it worse ,, that says (to me) that is must be electrical , and I think you have diagnosed it yourself now .
Good luck

Not quite that drastic, I meant to write plugs. I have 6 very dark brown plugs with soot at the bases. It's too dark to do any more tonight, I will round up a coil tomorrow

Thanks for all the help so far and stay tuned for the conclusion

No ballast resistor hmmmm,,,,what do your points look like now?(a little toasty maybe?)
I think re-coiling may bite the problem in the bud (be sure to use a ballast if not changing to electronic set-up)

I am happy to report that a new can of oil with a spool of wire inside it did the trick. My truck runs like the wild beast it is all 67 mules!

A great big thank you to one and all for the input and advise on this problem.

Now that the old girl is running strong, has new bearings in everything from the flywheel back and is quiet, it's time to spend some quality time driving her!