UPDATE:

I finally installed the guages tonight and I tested the vacuum line to the FPR with a vacuum pump. The line doesn't "hold" vacuum very well...but after a quick cruise with all the guages pumpin'.. the fuel pressure rises 1:1 as it should. I drove it "nice" for most of the test drive just to get a good solid reading on the wideband - as I said before.. it holds 13.5-14.5:1 at steady throttle. I barely got into it a few times to find that once it stumbles it jacks up the wideband so bad you can't tell what it's doing.

It "appears" to be the added boost brings the fuel pressure up and once it gets to a certain point it starts to misfire and the wideband goes nuts - up and down between 12:1 and 20:1 I know that it can't be running that lean obviously, which means the misfire is pumping raw oxygen into the downpipe and the sensor is picking it up as a overly lean condition.

I drove nice the rest of the way back and kept an eye on the AFR, still hovering perfectly in the 13.5-14.5 range on the cruise back. I let the truck cool down some and pulled the #1 plug... I had expected to see a bleach white plug.. instead.. I got a plug that looked like it had been spray painted black. Friday night I'll come home from work and jet it down some and give it another shot.... I guess it's so rich that it misfires, freaks out the WB02, and won't run. We'll find out soon.

 

this happens more often than not... you definitely can be so rich that it fakes out the wideband.

 

Well.. I got to talk to Kevin today and per his recomendation I pulled the powervalve out and put in a plug to "test" it out. I also added 7 jet sizes to the front, which is semi-counter productive I know. It felt a bit better, no doubt. The A/F was still jacked. I came back and put the PV back in, drove it again. MUCH better (keep in mind this is with the additional jetting AND the PV in place.) 3rd test drive - added 7 jet sizes to the rear as well, repeat test drive. MUCH BETTER! If you "roll" into it in high gear it pulls like mad and the A/F stabilizes at about 11.7-12.0:1.

The only remaining problem is that it if you floor it, the truck will try to die or stumble...but if you roll into the gas pedal.... it's fine.

I'm thinking it's the "low" locked timing, I might go a test pull or two and see for sure. Tomorrow night is the dyno session!

 

Maybe try a larger squirter in the rear? I think thats what fixed a similar problem on Craigs Firebird awhile back.

 

Well, aside from the stumble, I have to wonder about the jetting. I don't like the fact that I had to add that much jet to make it run properly. I just can't believe that Kevin may have missed the setup by that far, considering the other stuff I've used of his was always spot-on. Even after exchanging a few PM's from Brent, and before he knew of the jet sizes that came in the carb, he mentioned it should have near a 68/84, or something to that effect. Sure enough it did. (not that I expected any different!)

My main concern is to be sure I'm not masking another/different problem by adding so much fuel to it. The truck has a timing tape on it, I am going to pull #1 and verify that the 0 is actually TDC, or as close as it can get. Also, I was laying in bed thinking about it, I think the stumble is self induced. I noticed the accelerator pumps had tension on them. I tightened the screws to relieve some of the tension, but may have gone too far. That part should be a simple fix. I just want to be sure I'm not missing something on the fuel problem.

 

You might be thinking it can't be that lean because it would of damaged the engine. But if you have the timing low enough, and I think you do t it does not have enough timing with the lean condition to cause the damage, also because your taking it easy on the combination. I have not read everything yet, but it seems like adding jet and fuel is solving your problem. I will keep reading. Good luck, sounds like your getting close.

 

Yeah, That was the exact line of thinking I was using. As you read, you'll see I added jetting.. and it helped.. well.. you'll see the rest.

 

This is what I am thinking also. I had the same problem, and a little more aggresive pump cam and squirter change did the trick. Good luck!

 

This issue seems somewhat similiar to what I experience. Would it stumble if you rolled onto the gas?

 

Nope, not really. I am pretty sure the stumbling was due to me jacking with the adjustment on the accellerator pump. They had a lot of constant pressure on the arms, so I adjusted them (tightened) quite a bit.

The part I am worried about is the amount of jetting that it took to get it inline. I guess the climate had some to do with that - it's been about 25* during most of the test drives.

 

The correct way to adjust the accelerator pumps is back off the adjustment on both pumps with the bolt and nut arrangement using two wrenches. Then tighten the primary pump spring assembly until the lever is touching the cam and just touching the accelerator pump lever. THEN open the throttle to wide open, grab the accelerator pump lever with your hand or a pair of needle nose pliers and see if you have some clearance when the accelerator pump is bottomed and the throttle is at wide open. You want at least .015 more travel (but that really isn't much air gap) so if I see some daylight between the pump being bottomed and the throttle lever at wot I know I will not hurt the pump diaphragm and I will have some thermal allowance for heat expansion of the pump.

Hesitations on tip-ins of the throttle is due to the adjustment of the pump 90% of the time and the wrong sized shooter (too small) 10% of the time.

JMO

Tom V.

 

Man the only reason that I can say that you had to add as much jet is the same reason I had to for mine. Every engine is different and requires XYZ amounts of fuel. My CSU750 came with 68/78 jets and it was extremely lean and wouldn't really make any power at all. I added jetting to 75/85 and it made 845 RWHP, then added 75/91 on the very next dyno pull and it made 888 RWHP, so we all can clearly see that adding fuel via jetting, that it made more power.........same boost, same timing too. I took just the primary down to the recommended jetting to basically 70's up front and it blew a head gasket >. I should have paid attention to the LM-1 which was already telling me that the engine was going lean......oh well, you live and learn. Adding the jetting like that worked but it was a bitch to drive because my car stumbled way too much that it wasn't fun to drive at low speeds. I tried everything under the sun except for the new CSU BRPV's so I pretty much made my own stuff.

What jetting is in it now? Bump that total timing up to see if that'll help out some. As you can see, you've added fuel and it helped so the chances are, you won't be going back to stock jetting. Just read what that LM-1 is telling you or the plugs and go from there. Ask about the BRPV to see if that will be an option from CSU.

 

Well, I found out what the root cause was. The distributor was in 1 tooth off, throwing the phasing out of whack. I fixed that and it was PIG rich. I put the carb back as it was from CSU and made a semi-full pull on the dyno to see a 11.7-12.2:1 across the board.

It still has that lean pop through the carb at part throttle accelleration, it's really annoying! Right before it pops it sees about 15.5:1, which is the tell tale of leaning out on tip in. I'm not totally sure the locked out timing isn't contributing to that either... Tomorrow after work I am going to raise the timing to 36* and drive it to confirm whether or not it's a problem. Other than that the only thing I can think of is the valve springs... towards the top of the run, probably near 5500 or so, it bangs out pretty good.

Even with the bucking it managed 468/530 through what I'd consider to be a loose converter. I'll keep ya posted on the progress tomorrow.

 

Good, you are on to something then. At that tip in, just go up on squirter size to give that extra bit of fuel to help richen it up a bit.

Most of the time we get all hung up on the carb being the culprit but so far with you getting the distributor checked out, the new jetting made it too rich, so basically the carb mighta been in the ballpark with the stock CSU jets. You'll get it and as you said, check it all out to include valve springs. Fugged up valve springs too can cause you to overload the carb with jets to bandaid that problem. I've seen that too many times already. Good luck and that did make some great power to still have problems . I bet that damn truck is going to fly.

 

Yeah, I must admit I was thinking the carb the whole time.. when in fact it was the rotor phasing/distributor clocking was the main problem.

I hope it's not the valve springs, that means I have to work on this thing again! >

I'm going to test the timing theory, and I had thought about the squirters too - I'll give that a try since it's an easy fix.

 

Dave - what were the symptoms when you had the timing locked out low like that?

 

Interesting, I'm gonna give it a shot when I get home today. I'll let you know how it goes.

 

Well... I tried the added timing (locked in at 34*); No workie - exactly the same. I also changed/adjusted the squirters... I went as big as 37/45 with no change AT ALL.

As long as you don't get past the "tip in" point - it's fine.(which feels like right when it starts to click the secondaries). Kevin actually called me today to talk about the carb to see if I had tried the above mentioned things... He also mentioned the BRPV again, I just might have to give this a try.


Oh... and for anyone who was wondering what this monster is... or haven't seen it just yet...

 

Damn Brooks!

#ad
#ad