My car has this hesitation when I stomp on the gas at any speed. It cuts out. At times I'll be at a light and I might not see the light turn green or something, then I hit the gas and kill the motor. I want to take it to the track just to see what it can so but I think I should cure this first. I'm a mile high (denver)...and at times it smells too rich but at the same thime this seems like it isn't getting enough fule?????????? any insight would be apreciated. Thanks, JC
Is the carb a vacuum secondary type and where do you have the distributor vacuum line hooked up. There are two ports. You need the port that gets the vacuum signal from above the throttle plates. The accelerator pump cam in place? Does it squirt fuel right away when the throttle on begins to open? Is the fuel bowl level correct? In one or more of these areas you should find the problem.
i don't know It's a new holley 600 from Checkers. P/N 0-80457 The distributer advance is hooked up right, everything is, as far as I know. Accept the secondaries...I don't know if its vacume or not? I think its mechanical. The accelerator pump linkage, or cam, is in it's place. Would a hi-po accelerator pump help? This car is a daily driver and I'm trying to keep the mpg down. like i said at times it smells rich. Before I changed the jets to a smaller size I think it always smelled... Maybe I need to go down another/2 sizes? The floats may need adjusted I'll check that this weekend. I might add it's an 89 motor and geared with carap c-4 and 2.79 8" The gas mileage is around 14 - 15 mpg. Most of the driving is sort trips so I don't have a highway mileage. Even then when I get on the highway I get on the highway....alot of the on ramps here are short. I'm starting to get sick of working on it at times. I just wan't a few things sorted out and this is one of them. keep giving me ideas and I'll check it out. Thanks so far, JC P.S. no vacume leakes but I'll check again.
Don't give up on the problems. You are adapting nonfactory parts so there will be tuning issues to solve. A vacuum secondary carb will have a large diameter cap with 4 cover screws located on the left rear side. This is an area that contains a spiral wound spring and a diaphram. The spring controls the opening point of the secondary throttle plates. Note that a spring that allows the secondary to operate to soon will give feeling of power bounce when cruising along and suddenly calling on wide opn throttle. This feeling is actually a momentary stumble before the engine picks up the power. The correct spring allows a smooth power increase without the belt in the back feeling. A mechacial type does not have this feature, so can cause the engine to stumble if the throttle were to be opened quickly at low rpm. Jetting will control cruise and relitive fuel milage but not a stumble condition in most cases. Very small jets could aggravate the condition. The plastic cam controls the rate of fuel the pump will shoot fuel for acceleration. Look at the lever and adjustment this cam operates and adjust to a cloose gap not nessarly to contact the arm but quite close. If you see improvement your on the right track. Carbs out of the box like that 9 time out of 10 will need to be tuned in because the Holley company has no way of knowing what engine combination it will be finally used on and so many engines it would be impossible set up to meet every installation. Another area you might look, at that can cause a stumble is the ignition timing. Often times, jazzing the throttle will cause the timing to retard for a short time and add to this situation. A timing lite look at it will show it up. Pump cams and secondary springs are available to tune the carb with. I have all the info on these cams and springs that is hard to find now. I offer this help to you because I have done this many times.
ok thanks It is a vacume secomdary then. The timing is another isue I have...it's never been timed with a light bcause I'm running a 68 timing cover. I just don't know enough. any tricks for adding a pointer? where did you say the carb up grade info was? Thanks.....JC
I can't quite remember what the 68 cover looks like. If the crank damper has the timing marks on it, figure a pointer of some sort to mount on the cover so it is reasonably firm. Find TDC on #1 cylinder using a piston stop in the plug hole to fix the zero setting at the damper. To do this, get the pointer mounted, put a piston stop in thru the plug hole so it will stop piston travel near TDC (after TDC) on the compression stroke. Mark the damper then rotate the crank backward to the stop again (before TDC) and mark the damper. TDC will be exactly 1/2 way between the two marks. Then set the pointer to that location. For Holley carb info, I have a 1972 Holley hand book with all the data on spring and cam performance as well as much other info. Seems the books now days don't give all this info at least the ones I have seen. The springs are color coded and can be pruchesed in a pack at a speed shop or thru mail order. The accelerator pump cams, the same way. There are at least 9 different cams all color coded. If you find you need this info, I can scan the pages and e-mail them to you. The pages are graphs of performance curves of these parts vs throttle opening, discharge rates, spring tipin points vs engine size etc. Make one change at a time to see the results and keep some record of what was done each time.
Before the blower, I was running a (new) Holley 80457s four-barrel, vac secondary carb and it was indeed a chore to get it tuned. Never could seem to get it right (backfireing, stumbling, etc) until I had the bright idea to check the brand-new MSD distributor advance springs... guess what? It had the heavy TRUCK springs on it and would never advance below about 500,000 rpm. Changing to the lighter springs suddenly made my carb tuning MUCH easier. Moral of the story? Make certain the ignition system is in order before fiddling much with the carb. I agree with Ken Merrings advice strongly! After I fixed the distributor springs, I found that the stock plastic cam on the carb was WAY OFF from what I needed. Turns out that the stock cam didn't start to kick in until about half-throttle. Our V-8s need that juice early-on. I ended up going with the pink cam and a slightly larger main jet. Here is a good case for getting a jet and cam kit from Holley, really nice assortment. Anyways, after these simple changes "Pegasus" ran like a bat-outta-hell! Regards, Tracy
k Nice! my distributor is a new/recoditioned 78' duraspark and bronze gear. the ignition is an MSD 6al...which I thougt would solve the problems. The cam on my carb is burgundy. Can I down grade the vacume advance sping on my dist? main jets are #63...came with #65...rear metering plat is stock holley....the specs i got online said that the main jets were #64 but they weren't. Thanks for you in-put I will get under the hood soon but I basicaly haven't since this post or even longer ago. In the past I would post a question and run out work on the car. Now that I'm back online and working alot it's not the case.
One thing nobody's mention or I missed it is the dreded power valve. Occording to the holley catologe if you have a stumble when full thorrotle is applied and it doesn't matter what RPM you start at it is more than likly the power valve. The power valve only works in that aplication the manifold vaccum drops the power valve opens and give extra fuel so the rest of the systems have time to catch up. I had a similar problem with the wife's maverick I changed everything in that carb looking for the problem. I found out it was the springs in the distributor that was the problem. Now the carb is back close to the box settings, yellow secondary spring, brown pump cam(the only two changes), 6.5Hg powervalve, 65 main jets, 31 pump nozzle, and stock secondary plate. Moral of the story check the timing and distributor first
great I don't think I'm working this weekend....will a rebuild kit get it? I might as wll change the spring on the vacume advance too. I think this the right track thanks.....JC
