Backfire
#1
DIRTY RX
Thread Starter
Backfire
I've got a 12A with a Mikuni recently installed and I'm getting a backfire when I shut the car off. I've tried adjusting the timing and the fuel pressure but it still backfires. Anybody have any ideas?
#2
Full Member
Join Date: Apr 2002
Location: Ventura, Ca
Posts: 227
Likes: 0
Received 0 Likes
on
0 Posts
What's your exhuast setup? Did you get it pre-jetted for your engine? What's your setup; stock port or street port? What have you set ignition timing too? How does it run, do you have good top end power, or does it bog out or miss? Same with the bottem end...
Stock fuel pump?
Fuel Pressure wise you should be running 4.5psi.
Matt
Stock fuel pump?
Fuel Pressure wise you should be running 4.5psi.
Matt
Last edited by someone82; 11-13-02 at 07:23 PM.
#6
Full Member
Join Date: Apr 2002
Location: Ventura, Ca
Posts: 227
Likes: 0
Received 0 Likes
on
0 Posts
Get a guage and check out what the fuel pressure is at. You can pick up a cheap one at your local store and at least get an idea.
One question i didn't ask is when the last time the carb was rebuilt because if it hasen't been rebuilt in a while fuel could leak through the bowl and down into the chambers after being shut down... leak in the exhuast chamber, hit the exhuast and go BOOM. I've seen that before in a few old carbs. Which also happened with my old nikki carb.
Try running Racing Beat's timing:
L 2* BTC
T 19* ATC
this is done at idle
matt
One question i didn't ask is when the last time the carb was rebuilt because if it hasen't been rebuilt in a while fuel could leak through the bowl and down into the chambers after being shut down... leak in the exhuast chamber, hit the exhuast and go BOOM. I've seen that before in a few old carbs. Which also happened with my old nikki carb.
Try running Racing Beat's timing:
L 2* BTC
T 19* ATC
this is done at idle
matt
#7
DIRTY RX
Thread Starter
I give that timing a try and I'm getting a F/P guage tomorrow. As far as I know the carb hasn't been touched in at least 4-5 years. That could be a problem I'll have to fix.
Trending Topics
#8
Full Member
Join Date: Apr 2002
Location: Ventura, Ca
Posts: 227
Likes: 0
Received 0 Likes
on
0 Posts
4-5 years... yeah I think it's rebuild time... now only if I knew where to get a rebuild kit for the mikuni's
I'm running racing beat's street port settings and I've tried other settings and this is the best I've run so far
matt
I'm running racing beat's street port settings and I've tried other settings and this is the best I've run so far
matt
#11
standard combustion
Join Date: Dec 2001
Location: Twin Cities Minnesota
Posts: 1,374
Likes: 0
Received 0 Likes
on
0 Posts
I had this issue once when I was using my mikuni way back when. It turned out to be a issue with a couple pin-hole leaks near the rear muffler. It would backfire sometimes when letting off the gas. But mainly, it would backfire one loud one after shutting it off. Usually it only happened if you didn't let it idle for a little bit before turning it off.
#13
DIRTY RX
Thread Starter
I think I do have an exhaust leak at the flange by thr muffler. As soon as I get the guage set up today I'll know my pressure. I'd like to get a a/f mix guage but they're expensive.
Thread
Thread Starter
Forum
Replies
Last Post