JoeinCA Posted September 9, 2003 Share Posted September 9, 2003 Hey guys, I was wondering if someone near me wouldn't mind coming by and helping me tune my carburetor. I have a Holley double pumper 750. ( i think) The carb just spews streams of raw fuel whenever the throttle moves (duh) i think that it is running too rich thought i dont notice any black smoke out of the tailpipe ... I am getting a bad stumble at low RPMS, and it does not seem to want idle smoothly under load unless i shift into nuetral and back into drive. I think that this may be due to a poorly adjusted TV on my 700R4. I think that the locking converter may be engaging itself in all gears, and is only disengaging when i shift. I am unsure on this though. I am going to have to tune the car for the elevation change that i am going to have, and if it is running too rich at this elevation, it is going to be WAY too rich at 7200 ft. So, if anyone has good hands on experience with this stuff and would like to give me a hand, it would be much appreciated. thanks for your time, Joe Quote Link to comment Share on other sites More sharing options...
Guest zbot43 Posted September 9, 2003 Share Posted September 9, 2003 Ok, I live in Millbrae which is not that far from Antioch. I have been there and done that. Actually I use to work at carburetor shop and now I seem to do most of the carburetor adjustment work in my area. If it is a problem car they send it to me. 1st thing I know about your setup. The stock 700r4 torque converter is fairly tight, that is it engages at a very low rpm. You've probably got to much load on your motor in gear with your choice of camshaft. I have a toyota landcruiser with the same setup, but with a cam for serious lowend, and it works perfectly all day long. The stall speed works great with the weight in that vehicle. But I had a crane 272 in my Z, and experienced all the problems you are talking about. The 1-2 shift was so harsh you would have a sore neck if you did too much driving. And if you set the Tv cable up to make it loose enough so that you could stand it, you would end up burning the clutch packs. I wanted to keep the cam I had, so I switched to a 5speed that was given to me. If you need help with the carburetor I would have no problem helping you there though. I am very familar with the 750dp. The biggest problem you are going to have to overcome is the load on the engine at a stop. If you had a way to look at the fuel mixture, check it in gear and in neutral at a stop. I bet you would be very surprised. Usually you would set a mixture of around 1.5 - 2 % co at idle. If you made your adjustments in neutral or park, and then put it in drive I would be surprized if you had .5 % co. It won't want to run like that. Now if you compensate for the load and adjust in gear, when you start to accelerate you will have a flat spot, because of the overrich mixture you set at idle. I guess what I am trying to tell you is that you should look first at the transmission, and the cam you have in your engine. They have to be matched. Oh I almost forgot. I took my 700r4 out for a while and ran a 350 with a higher stall speed torque converter and it worked great. It just didn't have overdrive and that sucked. My 5 speed has overdrive and none of the problems. Sincerely, Marcello Quote Link to comment Share on other sites More sharing options...
spdsk8r Posted September 9, 2003 Share Posted September 9, 2003 I will soon be in this same position of tuning a Holley DP carb. I also have a 700R4. Doyou think a 2200 stall converter will be enough to overcome the heavy load at idle? My cam is a 488/510 lift 228/238 @.050 Dur. Quote Link to comment Share on other sites More sharing options...
JoeinCA Posted September 9, 2003 Author Share Posted September 9, 2003 I think you are dead on right about the cam. I was told the engine has an "RV" cam, or whatever the hell that is. I personally like to have numbers like lift and duration, but i couldnt complain too much, i got the engine and a TH350 dirt cheap. if i had the cash to spend, i would just put a 5 or 6 speed in. I like the t5 alot in my buddy's camaro. Zbot, I have very little hands on knowledge of carbs other than q jets and motorcycle carbs. I know that you need to go down a jet size for every 1000FT of elevation you gain. But i dont even know how to change the jets in my DP. I have the flat spot you are talking about on acceleration, the car loves 1/2 throttle to WOT when i stomp on it, but until 1/2 throttle it bogs. if i only had 3 grand, i could have a nice 6 speed and fuel injection. This 700r4 is annoying me, it's been nothing but problems...oh well... at least i left my clutch pedal in place but i'll have to move my vaccuum canister. I guess i'll have to wait and tune it in wyoming... unless you can help me get the correct jetting. thanks for your time, Joe Quote Link to comment Share on other sites More sharing options...
Guest zbot43 Posted September 10, 2003 Share Posted September 10, 2003 Sorry, It took me a while to get back. Somehow all the messages from the board were ending up in my junk mail, so I didn't see that you had asked another question. I would honestly look for help on the jetting when you get up to elevation. Trying to calculate the change here, and being there are totally different. But any problem you have here will usually be amplified at elevation. Too rich is way to rich, which is how holleys usually are set up. I bet we could get it running a lot better though here, and when you get to elevation the changes would be minimal. With what you said in your last comment about up until 1/2 throttle you have a problem sounds like it is all in the mains, and secondaries aren't a problem. So we need to change the primary jets, and/or acclerator pump jet. Neither of which is a big deal. Just need some gaskets, and some jets. And double check that the float levels are set correctly. Can I ask how many turns out are the idle mixture screws? This will give us an idea of how far off the main circuit is now. And in regards to the 488 Cam. Hard to say exactly without all the specs for the cam. Where is the power band for this cam? If it doesn't start until 2000 rpm, it would probably not be a good cam to go with the 700r4. With a manual trans no problem. The Low end torque type cam is what you want. The one that can idle at 500rpm. You want, and need to run the idle as low as you can. So the torque converter can slip, and it takes running it really slow to do that on the 700r4. When it is slipping it is not loading the engine, and there is no problem. Z cars weigh so little in relation to the cars that the 700r4 came out of (monte carlo, etc.) and all the valve bodies were adjusted for these cars. A transmission that works in one car doesn't necessary work correctly in another. Quote Link to comment Share on other sites More sharing options...
JoeinCA Posted September 11, 2003 Author Share Posted September 11, 2003 Zbot I dont want to be a nuisance, but do you think you could come by my place and show me how to tune the carb this weekend? i can go buy a rebuild kit for it so that i can have all of the necessary gaskets... i have extra z stuff that you might like... for your trouble. if it isnt possible, i fully understand... it is asking alot.. thanks you very much, Joe Quote Link to comment Share on other sites More sharing options...
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