I finally got the engine and tranny in took her out for a couple runs, the engine seems to run great except when I really get down on it. She starts cutting out at high RPM. Also I do not have a tach and the engine seems to be hitting a extremely high rpm before it shifts out to the next gear. The modulator valve came with the tranny which has a shift kit in it. I have never had a tranny with a shift kit and have never adjusted a modulator valve, but wonder if it wouldn't be better to just replace it. If I do will I have to adjust it and if so how???

Sorry about the ton of questions. Also I want to ad that I have not put the exhaust on yet. I am running stright out the Flowtech headers. Not sure if that could be the problem or not.

Thanks
Gary

 

I had the same problem with my c4 I would shift really late.

The problem may be because your shift kit isn’t matched right with the transmission. you can back the screw out 1-3 turns on the modulator. It is inside where the vacuum hose connects I believe. This will solve your late shifting problem and will also mitigate your positive shifting so you’ll be back to stock.


As for cutting out at high speed I bet your fuel pump isn’t keeping up with the fuel demand. Does it run fine all the way though first then cut out going into second? Does it feel like a rev limiter cutting spark to 4 of the 8 plugs? Does it still run fairly smooth just with no power? If so then get a carter high volume fuel pump / check filter.

Gun

 

Gun Jam,

Thanks for the info. I have not looked at teh modulator valve yet. I plan to get around to it in the next day or so.

As for as the cutting out I thought it was the fuel pump as well. I have an electric pump on it now that I got from Advanced. I that is what it feels like. The pump whas cheap, $34 bucks, I got it becasue I could not get the Edelbrock to pump. I bought the Edelbrock on line from a guy who claimed it was new, but I am not sure. I will try to upgrade the pump and see if that helps after I try the adjustment on the Mod valve. You mentioned if I adjust the screw out 1-3 turns will take me back to stock. If I only adjust it say 1 1/2 what will that do?

I am thinking about just replacing it, since the one on the tranny came with it when I bought it. It was dirty plus I did not plug the valve before I pressure wash the tranny and engine. Everything else seems to work fine except the late shift and the cutting out. The cutting out does nto happen all the time, about 1 out of 3 time I punch it.

I am not sure I mentioned I installed a Procomp Distribitor, coil and ignition box. I adjusted the rev limiter switch to 8K but no change.
Thanks
Gary

 

you should get a fuel pressure gauge. I have one for my 66 I measure the pressure right before it gets to the carb. Its fully mechanical an important gauge as far as im concerned, im getting 4-5 lbs cruising and 2 lbs under full power up a hill.

as for the modulator if you split the line (ie try for the best of both worlds) you might be able to get acceptable (on the high side) shift points with say half the loss of your shift kit performance.

If you get a new modulator it will probably still need to be adjusted but you will know its working right.

Gun

 

Mine will cut off like that every once in awhile when you punch it, it could be a misadjusted carburator or timing. I know thats what i problem is.

 

you mentioned that it feels like it is shifting at too high of rpm....Running straight headers makes it feel like higher rpm's than it actually is....try putting some mufflers on there and see how it sounds

my 289 used to cut out at high rpm's and it turned out to be a bad vacuum advance.....they only cost like $18 so that may be worth a try

 

You should be able to tell by the speedometer if its shifting late (assuming no radical gears) if your going 50mph cruise and its still in second then yeah its shifting late.

driving easy it should shift 1-2 (5-10mph) 2-3 (30-35 mph) for stock setup

Gun