Backfire through exhaust

Tiny
SHANON PETERS
  • MEMBER
  • 2002 ALL OTHER MAKES ALL OTHER MODELS
  • 1.0L
  • 4 CYL
  • RWD
  • MANUAL
  • 12,000 MILES
I have a 2002 kawasaki zr750 H-2, with a T4 with 4 keihin c/v carbs, which is backfiring through the exhaust, Yesterday it ran normal as Ive ever had it, but today it wouldn't start. It turns over everything sounds fine but it just won't start. Did I adjust the carbs to rich
Tuesday, August 30th, 2016 AT 6:16 PM

8 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check compression, when you pull plugs look to see if they are wet. Is this fuel injected or carb it may be injected. If backfiring through exhaust check for a bad plug wire or worn cam as the valve may not be opening. Compression should be with in 20% of all cylinders if not then there is an internal problem.
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 12:45 PM
Tiny
SHANON PETERS
  • MEMBER
  • 4 POSTS
Well the only problem I see today from yesterday is the #1 cylinder sparkplug wire boot just came off the wire but that never stopped it from running before. I don't have a compression tool to check for compression issues. Also no injectors just carbs. I pulled the plugs all 4 where black so it's rich, but when it's running it acts like it's running horribly lean rpms linger, runs really hot, blueing of the headers. It shoots flames like the 4th of July fire work show so that's a sign of running too rich. Now it won't start, turns over with no problems but it just doesn't seem to want to fire up.
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 1:25 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
I take it this has been modified and not a stock engine as it should have injection on it. Email back on exactly what has been done to the motor compression tool can be rented from auto parts.
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 3:42 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
I'm thinking a car not a bike sorry if it blues the headers it may be running to lean sounding like an exhaust problem. Try a new set of plugs if this has been modified then let me know
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 3:48 PM
Tiny
SHANON PETERS
  • MEMBER
  • 4 POSTS
From what I'm aware of the bike is stock, nothing has yet to be done with it. Spark plugs are black as night but it seems like it's running real lean. When it does run and I'm coming to a stop light it back fires constantly untell I come to a stop maybe that can help a little. So I tried to adjust and sinc the carbs without a mercury guage and now it won't run. I got a few large backfires the next day trying to start the bike up and it would not even try to start. Like I said it turns over like a dream sounds like it has compression but it just refuses to start up. Hopefully this will give you a little better of a description
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 4:13 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
First thing is to start over on carbs adjust them all the same if you have enrichened the carbs via needle valve then put them all back where they were when you originally started. Put new plugs in as well 1 heat range cooler, being a jap bike use NGK plugs or Nippendoso or whatever came with them. If there are no restrictions in header make one up to do it as you may have no back pressure and it's causing the problem. What it would do is die out around 3-4000 rpm then rev up again with no problem. It may also do the what you think is backfire but may not be. If you have any broken plug wires replace them with at least 7MM wire, preferably 8mm and NOT ACCEL I have never had good luck with them. I am assuming it has electronic ignition. Also check all your fuses as one may be burnt up that is for ecm/engine.
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 4:50 PM
Tiny
SHANON PETERS
  • MEMBER
  • 4 POSTS
I checked the fuses; all where good, wires need to be replaced I do know that it's just ignition coils since its a bike. I've also tried to put them back where they where when I started. 1:1 turn out, 2 same, 3 like 9 turns out almost not in the carbs anymore and 4 is 1 turn out. This is why I even attempted this pain staking process because of the 3 carb plus it was rich before hand anyways so I thought maybe I can make it right. Who ever had it before me ran it into the ground precentive maintinance wise and droped it twice had bolts in breather tubes of the carbs and everything. I managed to get lucky and get it running right just 2 where rich and 2 where lean so I tried to adjust them equal like they are supposed to be and aparently I did something wrong
Was this
answer
helpful?
Yes
No
Wednesday, August 31st, 2016 AT 7:21 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Well you need vacuum gauges to do any adjustments on this carb wise. here is a thing on you tube on how to rejet these carbs if it's a Keihin carbs factory setting for air is 1.5 turns..
https://www.youtube.com/watch?v=ozsdPgVJI5Q
Was this
answer
helpful?
Yes
No
Thursday, September 1st, 2016 AT 6:32 AM

Please login or register to post a reply.

Related Engine Backfire Content

How To Fix an Engine Backfire
VIDEO
How To Fix an Engine Backfire
In­struc­tional re­pair video
Backfire Repair
GUIDE
Backfire Repair
When your en­gine back­fires it can do so in one of two ways. First and the most com­mon way is when the en­gine is run­ning a small ex­plo­sion of un­burnt fuel is ig­nited in­side...
VIEW MORE