Yeah, I got the thumpur, love how it sounds. Idle is pretty bad. I got a stall converter 2000-2300 put it in yesterday. Idle a 900 drops to 450. What could be wrong? Do I need 2300-2500? There are no vacum leaks, carb tuned right. all else is running great. Guy's with Thumpurs what did you do to get it to idle right?
Yes, you definately need to put a timing light on that thing. While you are at it, check your total timing after 3000rpm or so. Your initial and total timing numbers are basic variables you NEED to know when doing any troubleshooting. Good luck, -Abone.
Do you mean 900 in neutral or in gear, if thats in neutral you need to set the idle up so it runs about 800-900 in gear..if not what do you mean it drops to 450??
with a bigger cam your idle speed needs to be increased. With a big cam, I like around 1150-ish in nuetral. Its not uncommon with some big cams to have to go to 1200 RPM+. try increasing your idle speed some. Scot
I have the idle speed at 1,000 at neutral, when I put the car in drive the idle speed drops to 400. It is doing this with a 2000-2300 stall converter. It was doing this with the stock converter. The timing is set at 12 intial 36 total. The carb is set with a vacum gauge. With a 2000-2300 stall isn't it supposed to slip a little and engage at about 1800. In drive the car shakes. there are no vacum leaks. could it be the balancer?
Does the exhaust smell rich at idle, like you were running with the choke still on? What kind of vacuum will it pull at idle in neutral? The power valve or power pistons may be enriching the mixture at idle now, even though there's no load on the engine. You might be in for some more carb mods. As stated already, keeping the initial timing up will help improve the idle. The high stall convertor can't do it all. The increased stall speed won't really be that noticable at idle. If you've got vacuum advance on your distributor, make sure it works. If it's connected to ported vacuum you might experiment with it connected to manifold vacuum, though you might have to take out a bit of initial timing.
A converter with a stall speed of 2000-2300 is not going to act any different than a stock converter. That extra 1000 rpm of stall comes into play under load at full throttle. The load when you put it in gear at idle is as much the pump applying line pressure as it is the converter. If you are running a points ignition make sure the DWELL is correct ( dont use a feeler guage) then set timing.
Sometimes the timing marks arent right. Time it by hand if you have to to check it out. Get the highest idle by moving it back and forth. Also where is your idle screw set at. Is it cranked all the way in or just a couple turns in. What carb do you have?
I'M RUNNING A HEI WITH A MSD 6A. The vacum advance is working advance can is adjustable. We are going to a 2300-2500 friday. How can I taylor my the power valve to the motor and cam. I have a vacum gauge what do I look for and what determines what power valve I use?
Your not even in power valve territory yet. Wheres you idle screw at. You might be out of the idle circute
Your power valve is usually matched to the cam by reading the vac at idle. For example: if you are pulling 8inches of vac, you should as a general rule install a power valve with half the value like a 4.5 What happens if you don't have the right valve to match cam overlap is the stock power valve is trying to open and as a result it will bypass the idle circuits causing a very rich condition. Over the years of running " big " cams, I have always adjusted timing, power valves, and I have also drilled my primary butterflies with a 1/8" inch hole to prevent fouling plugs. This is common in Winston cup, where they run large overlap cams to prevent plug fowling.Works for me everytime. Just my opinion!
I'm sure it's none of my business, but I've got to ask why. Has your current toque convertor failed or did you install a used convertor that was of unknown quality? Odds are that you're fighting an ignition, carburetor or tune-up issue. Here's a bit of info about using a vacuum gauge. A web search will turn up plenty more. http://autospeed.com/cms/title_Using-a-Vacuum-Gauge-for-Engine-Diagnostics/A_2393/article.html These articles tend to assumes a stock engine which will provide higher vacuum readings under most conditions. Running your "Lumpy-Lou" Thumper cam is going to lower these readings but this is the information you need to find out if you're adjusting the vacuum advance or changing the power valves or power piston springs.
How did you come up with your timing numbers? You can't go off the old balancer marks, as the Thumper cam is way off from stock, so timing marks wont even be close. Might look like 12 degrees, but it could actually be 10-15 degrees off, unless you dialed it in with a degree wheel to get a new mark for this cam's specs.
try running the vacumn advance to full ported vac,Readjust as necessary ,Also try the lightest springs in the distributor ,,,,,,Ran into this on a fireball cam ,
Stall converter was the answer 2400 was perfect. Great idle and the take off is unbelieveable. My hair is blown back I can't comb it forward. This cam is very powerful. It smokes the tires. top end is frightening. Beware of THE THUMPUR .....POKEY!
you need a higher stall speed about 2500 to 3000 11 inch converter at biggest.its gonna shake like a dog shittin razor blades at idle.isnt that what you bought it for?rumpity rump sounds) i ended up adjusting my initial timing to 20 degrees with 15 degrees advance in the distributor (35 total)i know it sounds goofy but it works
What Seb says. I don't understand the comment about "can't go off the old balancer marks". Changing cams won't have any meaningful affect on using the timing marks on the balancer. The cam may well require different timing to obtain best performance, but that doesn't mean the balancer marks shouldn't be used. With that cam, try an initial timing of 16 degrees set at a low around 700 rpm (with vac line plugged) to keep mechanical advance from being activated. Aim for around 36-38 degrees of timing (initial and mechanical advance), all in by 2,500 rpm without vacuum hooked up. Use full manifold vacuum.
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