GM Performance 350/290 motor question

[99-LS1-SS]

I have more information regarding my saga.

When I had the new transmission put in last week, I noticed an exhaust leak when I got the truck back. I figured they crushed the doughnut gasket that connects the manifold to the Y-pipe. I got under the truck and pulled the old one off and I was right, the gasket was shot. I put a new gasket on and the "ticking" got noticeably better but, it didn't go away totally. So now I have an exhaust manifold gasket leaking (I hope it's that and not a cracked manifold). I just ordered a set of Earl's Pressure Master exhaust manifold gaskets (part# 29D03BERL).

I am amazed at how many issues I'm having to wade through after putting a new motor and transmission in this truck. I'm ready for this thing to start running like it should.

Once I have the exhaust leak fixed, I'll recheck the timing then the air/fuel settings, the carburetor vacuum, and then I'll go to the pump nozzle. Does this sound like the correct order of importance?

On top of all of that, I have to adjust the governor because my low RPM shifts aren't right.

Ok, I'm done whining for now.

As always, thanks for all of the help! It might not seem like it but I have learned a lot through this process and I am grateful for that.

I'll report back in a few days.

[geezer#99]

I wondered what that whining noise was! Woke me and my cats up from our afternoon snooze!!
JK. LOL!!
You might think it never ends, but someday after you've adjusted the timing or tweeked the carb or changed that leaky oil pan gasket for the umpteenth time and it finally fixes it all, you'll wonder why it took so long. It's all just good experience.
It's all water under the bridge and in a few months when it warms up you'll get to tune your carb and your timing again. But you'll have a bunch more knowledge and it'll be easier. You'll do things in automatic mode and not even need to think what comes next.
THere is no secret for the combination of things to try. Just one at a time and keep notes on what does and doesn't work.
Keep pluggin' away! It's good for your brain!!
And now.
Back to your regular programming!!

[storm9c1]

Yep, each project is different. Some go like warm butter, others are just buggers that never seem to quit dragging on with problems (for no good reason too!).

I found out the hard way that doing it yourself is the better way because when someone else does it, you end up redoing half their work yourself anyways. LOL. At least that's been my luck. And I've also had to redo my own work half the time too. LOL. But at least I learned from those mistakes. I wouldn't know as much as I do now without going through all of these trials. Most of the time, the next project is easier. But sometimes it isn't because new things STILL surprise me all the time. The rewarding part is finding correct solutions to new problems (rather than bailing wire and duct tape).

You are on the right track.

[99-LS1-SS]

Originally Posted by storm9c1

I found out the hard way that doing it yourself is the better way because when someone else does it, you end up redoing half their work yourself anyways.

This is a very true statement.

[ayellow56]

A couple of things I noticed have not been mentioned here are float level and the fact that Crane made adjustable vacuum advance canisters. The float level will affect transition from the idle circuit to the part throttle circuit. Simply put a slight increase in float level up or down will effect the pull-over during transition. In your case I would raise the float level slightly to induce an earlier pull-over thus giving you a richer condition. So far as timing I would start at 12 degrees and fine tune,as others have mentioned, from there. I've been using adjustable vacuum cans for many years on all my SBC and BBC carb equipped engines . Crane was the only one that made them and I don't know if they stiil do. Good Luck. See Ya .Steve.

[99-LS1-SS]

I JUST found out that my distributor came with an adjustable vacuum advance. Yay, something actually worked in my favor! I'll be working on that soon too.

[storm9c1]

Originally Posted by 99-LS1-SS

I JUST found out that my distributor came with an adjustable vacuum advance. Yay, something actually worked in my favor! I'll be working on that soon too.

Keep in mind there are two styles of adjustable canisters. On the MSD StreetFire (cheapo), for example, some came with adjustable vacuum advance, some didn't (and the documentation changed along the way too). Some came with stop plates instead. What brand is your distributor?

If you are lucky enough to have an adjustable canister, then you have to see what style it is. One style adjusts the "rate" of pull depending on vacuum level. The other style adjusts the "limit" of pull. If you have the former, then you may still need a stop plate.

So make sure you check yours carefully.

[99-LS1-SS]

Originally Posted by storm9c1

Keep in mind there are two styles of adjustable canisters. On the MSD StreetFire (cheapo), for example, some came with adjustable vacuum advance, some didn't (and the documentation changed along the way too). Some came with stop plates instead. What brand is your distributor?

If you are lucky enough to have an adjustable canister, then you have to see what style it is. One style adjusts the "rate" of pull depending on vacuum level. The other style adjusts the "limit" of pull. If you have the former, then you may still need a stop plate.

So make sure you check yours carefully.

Can you elaborate a little more on the part that I bolded?

I'm thinking I probably have the cheaper version. I'll go check to make sure.

[99-LS1-SS]

This truck is turning into the gift that keeps on giving. I just caught a glimpse of the number 7 plug boot arching to the manifold. Dang it! This stuff needs to settle down. I need to drive this truck every day.

What is a GOOD set of plug wires?

[cableguy0]

I use Taylor wires on everything. The boots hold up extremely well near headers and the wires will outlast the rest of the ignition system. I use the cut to fit spiro pro 8mm wires because ignition wires hanging all over the place drives me nuts. I use looms that use the valve cover bolts and route the wires between the tubes. http://www.moroso.com/catalog/catego...?CatCode=40009 I use part number 72172 with small blocks. Taylor wires are part number 73251 for red cut to fit wires. They also come in a bunch of other colors.

[99-LS1-SS]

I have an update.

I got the size #35 and size #37 nozzles in today. My carb did come with a #31 nozzle, as I suspected. Tonight I installed the #35 and I also swapped the plug wires. As it turns out, I had 2 that were arcing. My exhaust manifold gaskets haven't come in yet so I haven't addressed that yet. I'll get to the results of tonight's work in a minute.

I've been obsessed with making this truck run better for the last few weeks. I'll go to sleep thinking about it and I'll wake up thinking about it. I suppose I probably have some form of OCD that won't let me have something that doesn't work correctly if I am able to fix it. Anyway, I was reading and thinking and I believe that some of my issues are coming from the fuel percolating in the bowls. That might explain why my truck died in the middle of stop and go traffic and it would explain why warm starts are so tough. I wrapped the fuel line coming from the pump to the carb in a foil based adhesive wrap. I also purchased a phenolic spacer that I'm going to install in the morning. Since I have a dual plane intake and I'm not going to be drag racing this truck I got the 4 hole version instead of the open version. I'm hoping that between wrapping the fuel lines and installing the spacer, I'll fix my warm start issues and dramatically reduce the chances of vapor locking this summer. I'll report my results tomorrow regarding the warm starts.

Since the transmission was installed I haven't been happy with the low RPM shifting. I have been on the phone with Hughes a few times and I've done all of the adjustments that they've recommended and it didn't help at all. The 1-2 shift wasn't happening until about 21 MPH and the 2-3 shift was coming in almost immediately after the 1-2 shift (somewhere around 25 MPH). Hughes ended up sending me a new governor and I installed that tonight. It shifts MUCH better. I think I can fine tune the shifting with the throttle valve cable now, where before it didn't affect the low RPM shifts at all. That's one headache gone!

Back to the nozzles and plug wires. With the #35 nozzle installed, the truck didn't stumble nearly as bad. It still has a slight stumble but, it is noticeably better. I think I'm going to bump it up to the #37 and see how that does. If that doesn't help it, I'll put the #55 power valve in that I got today. If the power valve doesn't help, I guess I'll learn how to re-jet a Holley 4150...lol.

I have an economy related question for the Holley experts. Given the fact that my truck is a heavy pig with terrible gears and tall(ish) tires, should I put a stiffer vacuum secondary spring in it to keep the secondaries from coming in so soon? I know percolation can can hurt gas mileage and I suspect that it is a factor in my excessively terrible MPG. I don't expect this thing to ever get good gas mileage but, it is horrible at the moment. So, do you guys think that a stiffer secondary spring will help, on top of fixing the fuel percolation will help my gas mileage?

Thanks.

[99-LS1-SS]

Progress was made today!

Instead of going up to a size #37 nozzle, I decided to leave the #35 nozzle in and switch pump cams. It had the orange cam in the number 2 position. I switched it to a blue cam in the number 2 position. The ramp rate of the blue cam is steeper than the orange cam, so the fuel squirt gets delivered faster. I also added a 1" phenolic spacer to help minimize the fuel bowl percolation. Between the spacer and the blue cam, my stumble is MUCH better. It isn't 100% gone yet but, it's 95+% gone. I think I'll need to increase the jet size for the primaries and the secondaries before it is totally gone. But, I can tolerate with the way it drives...for now.

I think my truck likes to make sure I'm never done showing it attention. After having significantly reduced the stumble, my truck decides to spring a small leak in the heater core. /sigh

So far, here is what has been done to my truck to help the 350/290 engine with Holley Street Avenger that has a off idle stumble in the order that were done in.

1. I set the initial timing to 14 degrees BTDC. Currently, I'm not running vacuum advance. I will hook it back up once I know I can control it.

2. I ran the air/fuel mixture screws in all the way and backed them out 1.5 turns to get a baseline. I ended up backing them out a total of 2.5 turns.

3. I set the curb idle screw down where it should be with the truck in gear.

4. I installed a 1" phenolic carburetor spacer to help reduce the chance of fuel percolation. I also wrapped the fuel line coming from the mechanical fuel pump with a heat reflecting foil wrap to help reduce the chance of vapor locking.

5. I changed the accelerator pump nozzle from a #31 to a #35.

6. My carburetor came with a orange pump cam that was in the number 2 position and I switched it out for a blue cam that is in the number 2 position.

These steps helped my off idle stumble greatly. While it isn't totally gone, it is much, much better.

[cableguy0]

There is more tuning to be done with the idle mixture. Just randomly picking a point to turn the screws out to wont help you. You need to slowly turn the screws until you get the highest idle. Once you adjust one screw and the idle rises bring the idle back down with the idle screw. Now adjust the mixture screw on the other side for highest idle. Turn the idle back down with the idle screw. This should be done in park. Not in gear. Truck should idle at 750-800 in park. Now with idle speed set recheck and make sure timing is still at 14. Don't be scared to put another degree or two of timing in it. It might clean up your stumble completely. A lot of tuning comes with experience and knowing what to listen for etc. The only way to learn is to just try different things. There probably isn't anything you can screw up bad enough that we cant help you get it straightened back out. There is a lot of years of experience that read this board and contribute.

[99-LS1-SS]

Originally Posted by cableguy0

There is more tuning to be done with the idle mixture. Just randomly picking a point to turn the screws out to wont help you. You need to slowly turn the screws until you get the highest idle. Once you adjust one screw and the idle rises bring the idle back down with the idle screw. Now adjust the mixture screw on the other side for highest idle. Turn the idle back down with the idle screw. This should be done in park. Not in gear. Truck should idle at 750-800 in park. Now with idle speed set recheck and make sure timing is still at 14. Don't be scared to put another degree or two of timing in it. It might clean up your stumble completely. A lot of tuning comes with experience and knowing what to listen for etc. The only way to learn is to just try different things. There probably isn't anything you can screw up bad enough that we cant help you get it straightened back out. There is a lot of years of experience that read this board and contribute.

I ran the screws out until I got the highest vacuum. I didn't do it randomly, I just forgot to put that in the list. I will try the additional timing too.

[cableguy0]

OK good. It read as though you just turned them out 2.5 just trying to save you grief. Good deal then. Do you know where your total timing is set? Have you put a spring and weight kit in the distributor? You will want 36-38 degrees of total timing. Most distributors have very stiff advance springs and don't allow the mechanical advance to come in near as soon as it needs to.

[geezer#99]

A curious question!
What gear or speed (mph) does this stumble occur at?

[99-LS1-SS]

Originally Posted by geezer#99

A curious question!
What gear or speed (mph) does this stumble occur at?

Any speed any gear but, it is more noticeable in the lower gears. It appears to be completely related to throttle tip in.

[geezer#99]

Bump your timing up to 18. See what that does.

[99-LS1-SS]

It still stumbled a little at 18 degrees. Given the fact that it stumbled at 16 and 18 degrees and I didn't feel any improvement in performance. Should I stick with 16 degrees or run it up until I hear detonation?

One thing I am going to do is, to get a quality adjustable vacuum advance can and put it on so I can run vacuum advance. I'm doing this because I hooked my current vacuum advance up and drove around and the stumble was gone but, I am not comfortable with how much timing the current can is adding. Also, I'm having trouble hearing if I have slight detonation over the ticking sound that my exhaust manifold leak makes. I hope to have the gaskets today or tomorrow and fix the exhaust issue ASAP.

I feel like I need to address the carb jets after the vacuum advance is taken care of. I still think this carb is running lean. I've richened it a good bit and I haven't seen a hint of black smoke. I plan on removing the secondary jets (they are 68's) and put them in the primary slot (they are 65's) and then I'm going to buy a couple of sets of jets for the rear that are between 4 and 6 sizes larger than the current secondary jets.

Does anyone see any issue with my current plan?

[68c10owner]

The 670 street avenger is known for this stumble. mine had it too. I had a 290hp 350 as well. Strong runner for what it was. Ended up selling it before I got it set up right. google the carb, tons of info on getting that stumble out. might have to jet up the primaries a bit too.

[99-LS1-SS]

Originally Posted by 68c10owner

The 670 street avenger is known for this stumble. mine had it too. I had a 290hp 350 as well. Strong runner for what it was. Ended up selling it before I got it set up right. google the carb, tons of info on getting that stumble out. might have to jet up the primaries a bit too.

I've come to learn about the Street Avengers stumble. I agree about running the primaries up a little. That is on the to do list. I will swap the secondaries too. I've googled this carb so many different ways and I've found a TON of useful information. Swapping the orange cam out for the blue cam helped a lot. I'll update this post when I get it worked out.

[Tomahawk30]

So I just found this thread as my 72 has the same engine w/ a similar carb (Quick Fuel HR-680) that I am trying to get tuned in. Where did you end up with your initial / total timing? Did you end up using your vacuum advance? How about your final accelerator pump nozzle size? Did you end up changing out your power valve too? Just trying to get a good idea of what worked for you.

I'm going through some similar issues, but I think I'm fighting a vacuum leak first. If I set my idle low enough that it is running only on the idle circuits, I have to set my timing no lower than about 14* BTDC and my vacuum bounces between 14 and 15 inHg. The previous owner (my father in law) had the 290hp Goodwrench engine installed, but they just reused the stock intake from the original engine. I'm using a squarebore adapter that I suspect is the culprit of the vacuum leak, but I might just buy an Edelbrock Performer like you used to install this weekend.

Any pointers about your setup that might save me a day (or an hour, or a few minutes) would be greatly appreciated!

Thanks!
Jake