Backfire Issue, need advice.
 

Hi Guys, Thanks for the advice last June on my blown up motor. I got the boat going about November. And it ran great. 489 strokers, Howards roller cams (part #120405-10) cast iron 049 heads with 2.19 intake/1.88 exhaust, 9.2:1 compression

About January I got a deal on a set of Weiand 256 blowers to go on my engines. I talked to various people and was told the cam was not ideal, but that it would work with low boost (4-4.5 psi) I'm running holley 0-9015-1 carbs with vacum secondary. 2 Carbs per motor. I have Holley pressure regulators, that are putting out 7psi. I was told I didn't have have to boost reference the carbs with this application. My HEI distributors would not fit the blower intakes so I got some MSD units with a traditional coil. They advance 18 degrees so I was setting the timing to 14 degrees at idle. (what do you guys recommend with my setup) I'm running super unleaded.

It doesn;'t want to idle, and when given throttle backfires thru the carbs and exhaust. I dont want to damage anything obviously.

I messed up last week and put too small an intake gasket on it (weaind blower intake large rectangular port, heads large oval port) and was blowing air/fuel/combustion out. Didn't take long to realize what I had done and now have the larger gasket on.

The plugs are super black from that screw up. I have new ones coming. Gonna try that and see what happens, but I don't think that's the problem.

Any thoughts? Thanks in advance.

Without being there to diagnose, my first guess is that You put the distributor in wrong (orientation wise) or you have some ignition wires on the wrong spot.

or the carbs are way out of wack.i don,t want to sound rude but you might be wise to get someone with blower setup experiance to help you.it would be easy to ruin the engines with a tune up that is incorrect.

To much fuel being delivered IMHO

Thing though is popping thru intake and exhaust.

Typically:
Too much fuel - exhaust backfire
Too little fuel - intake backfire

Way too early combustion - intake backfire
Way too late combustion - exhaust backfire

I've put wires/caps/rotors on chevy motors like a million times. I have installed wires in wrong position a couple more times than I'd like to admit. That's why I like to put # indicators on each wire when doing them. Easy way for quick confirmation.

That said, installing a distributor because of the oil pump drive shaft moving on removing distributor, many people install the distributor without turning the oil pump driveshaft a little, and end up a tooth off. Boom, boom, pop, pop.

Edit in: yeh, fuked up plugs can do the pop, pop too.

Yeah SB, I was thinking the same thing. Distributors not 180 out. We replaced the plugs with new ones. Wires are routed to the right plugs. All cylinders were firing, all plugs are equally black.

Roger that Mike. I know no one in my area with experience with dual carb blower setup like this.

That's what I'm thinking Mseuro.we went from a 76 main jet all of the way down to a 65, same thing. Hmmm...

Timing is WAY off or way lean. Popping through the carb is usually lean. When you give it gas does it pop and die or does it just keep popping?

I posted that before I saw your last post SB. Sorry about that.

I pump it twice before starting, When it starts it hits on all cylinders and revs like a nice normal startup, then starts this barely idle while backfiring deal, when given throttle, backfire and dies

All plugs look like this...

http://i159.photobucket.com/albums/t...psi0jv2gau.jpg

Sounds like a tractor...
http://youtu.be/E0amIJX5ibk

I'm going to throw some old school logic at you on this.

I would base line the timing at TDC with a static timing light...No1 at TDC and the distributor lighting up on the mark. Fire it up and let it run a bit. Then shut down...set up you timing light and start it making sure you don't see the timing mark wobbling around. Loosen the distributor enough to turn it a bit and bring it up to 8* BFTDC.

I think 14* initial is WAY too much. If this works...figure out what you want to have total advance at 3000 and have a distributor guy set those MSD's up.

I had a similar issue with my Vortecs setting them up and at the end of the day I found broken springs in both my distributors. You didn't mention the history of your distributors but if they aren't new...I would guess that's where your problem is.

You might call the guys at DUI in Memphis and talk to them about this. They have a "Small Top" replacement for the HEI's that might fit your set up. I sent my DUI's I bought on Swap Shop here to them and they set them up.

My Dad and Grand Dad always used to say that if air, fuel and spark all get there at the right time it will run good. Knowing that and 18436572,,,there is an answer to your problem LOL !!

Good Luck !!

roots blown engines like timing at idle.his suonds lazy like not enough initial timing,also sounds like it has a few dead cylinders.

Ok...roger that on the initial...but something still has me thinking distributors.

Your thoughts?

hard to say with a 21 second video.i would take the carbs apart and check them out before i started it again.also would check plug wires for resistance.

The carbs, distributors, wires, and plugs are all new if that helps at all.

i watched the video again on a computer with a bigger screen and better sound,timing seems retarted,i would recheck the initial timing as it seems lazy.

Thanks guys, gonna be hard to sleep tonight now lol
What would you recommend the initial timing be set at?

Read thru this thread: http://www.nastyz28.com/forum/archiv...p/t-64065.html

May send you in the right direction....or at least give you some info.

w/ engine running,look done the carbs,,see if its dumping fuel.sounds like it needs carb work.as for the 14° initial.thats not the problem.I've run blower motors locked out at 32°.

you say you have run locked at 32,and i also used to run locked dist but why do you say 14 initial is not the problem?i believe 14 initial is part of the problem,it needs more.

I just talked to Ricky at Holley. He said these carbs will never work. He said to get the 0-80592-s blower carbs. Eric from the blower shop recommended quick fuel 650's. In this application, do you guys worry with the carbs being non marine approved carbs?

Depends on how quick you are with a Fire Extinguisher. LOL

Seriously speaking...with marine Flame Arrestors your biggest risk is float bowl overflow and flooding the bilge with fuel.

How is is coming along now ? Certainly wish you well with this.

imo,650 is too small.i would go with 850,you really can,t over carb a blower motor.

Two 850's??

yes.

X2. You definitely need more carb regardless. I normally have a tendency to under carb however on blown application like Mike said. Also if you do end up with larger carbs go with DP.. Btw you went over everything very closely and have no vacuum leaks? You need to make a list and go through everything one by one.
Back to the carbs I wouldn't go anything smaller than 800's amd make sure their boost referenced. Just don't let the black plug let you think you have plenty of carb. That's just telling you something is way wring and not firing properly and carbs out of tune/timing etc.

Do a research on Google or even here on oso for similar builds and ck for normal carb set up. I'm going to experiment with a tunnel ram and two 700's on 496'. Set up is for 565 builds but...

Thanks for the input guys. I'm listening. But I think the carb size is not related to this problem. I think it would run on 600's or 850's. The holley 600 blower carbs came in. Installed them. No difference. Changed the plugs out to AC Delco R44T gapped at .045. No change. Plugs still black, backfiring out exhaust, and backfiring out carbs when given throttle. We're gonna change out the distributor and coil from right side motor and see if anything changes.

Or let me ask you guys this, don't you think they'd run on 600's? Or do you think that is part of this problem?

2 600's on each engine? Should be enough. Do a compression test, put a vacuum guage on it. Is this same issue with both engines?

Yes, two 600's. We just swapped the distributors and coils. Same thing. We're only running the left motor right now. These engines only have prolly 2-3 hours on them. All plugs are equally black. They ran strong in november. We havent run the starboard motor yet with a blower. I think we're gonna pull the blowers off and put the air gap intakes and single 750's back on and run it for a while. We're supposed to take it to the beach this weekend. It's getting down to the wire. I wonder if the cam is so far off for a blower setup that it just wont run??

I was going to suggest going back to naturally aspirated since you're in a tight time wise for your trip. If they run ok natural then you know for sure there is a bug in the blower set ups some where.

I dont think the 14 deg at idle is the problem. Mercs supercharged engines idled at less than that . It certainly will idle better, with more timing at idle, but not the issue with it blackening plugs, popping, and overall running like chit. Nor will the carb cfm.

I agree with mike t, twin 850s would be my choice if buying new

Are you sure you have all the valves adjusted properly? What procedure did you do when adjusting them ?

I read through most the post however may have missed a couple but if you haven't do a comp test and leak down. ck out your grounds... Sometimes it's just completely different than what you'd expect. Wiring harness? Mice? i hear what your saying with the carbs. Regardless of size this shouldn't be doing what it is plus you've eliminated that. Along with your grounds make sure any hot wire isn't touching or arcing anywhere.

Do me a favor and run it in the dark on the hose or whatever and look around for any of the above. Arcs etc show up well when the lights out plus you can have a beer while doing it. Just trying to help. Ck everywhere including your plug wires and plugs. Do it in the dark. Other thing is possible your throttle wires etc. neutral safety switches shorting. This could just be a coincidental deal going on and not related to your new good guy parts.

Ok, we went back to normally aspirated setup. Air gap intakes, holley marine 750's. The only "new thing" we had was the msd pro billet distributors, and the new plug wires. Cranked on Port motor (the one we've been playing with the whole time), same thing. We got the starboard motor read and fired it, same thing. We pulled the new plug wires off the starboard motor, and put the ones we ran last year on there. Same thing.

I went and got my old accel HEI distributors, installed on the starboard motor, problem solved. Shon''s wiring the old HEI in the port motor now. I'm not getting what the problem was. We had them grounded on the soleoid ground on the back of the motor. I never did check the ground with a meter, but good grief I don't see how it would not have been a good ground. Maybe I'll check later in the summer, and reinstall the blowers, but right now I'm satisfied just knowing it was something to do with the distributors, and the boats running right. (fingers crossed on port motor)

sucks that you jumped the gun and pulled the blowers off.

Fukin MSD. Excuse the french.

Rust, module issues....
Case in point, The other year some of their distributors where coming with the wires wrong in the connectors.

:cool-smiley-027:

Hei dui flame throwers here. Been down the other road and would always seem to be chasing something.

Everything happens for a reason is one way to look at it. It just wasn't meant to be at this time.

Port motor runs also runs awesome with the old HEI ignition. Got the timing set on both of them.
I know Mild Thunder, I hate that we pulled the Blowers off but at least it's running right now. And I had no idea what the problem was. I just can't hardly believe that two brand-new distributors were messed up. I had convinced myself that it had something to do with the set up, the Head's or the cam not working with the blower or something.

MSD - Might Soon Die