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Old 09-06-2008, 01:50 AM   #11
Lou
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Hey Shag, did you ever get the backfire corrected on your bike?

I am having the same problem. I have a MAC slash cut exhaust on a 1984 VT700. I also did the rejet, and replaced the filter with a K&N (as recommended by Dynojet), and the backfiring is ridiculous.

I've been adjusting my carbs on every ride, and I swear I have been fully seated, and up to 5 turns out, and I still get that damned backfire on decel.

I'm actually thinking about cutting the baffles out of the pipes to see if this helps.

The bike runs great otherwise. Can someone help?
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Old 09-06-2008, 03:17 PM   #12
lang
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sounds like your idle circuit could still be too lean. If you're getting popping on decel and you have to turn your mixture screws out more than 4 turns, I'd suggest you bump your pilot jet up one size. If I recall, the dynojet kit doesn't come with pilot jets (but I could be wrong) so you'll likely have to get the next size keihin jet.

Cutting your baffles out is just going to make you run even leaner - so don't do that. Also don't try fully seating your screws again either.

Listen, it really doesn't sound like you know what you're doing. It might be wise to just pay to have it dynotuned.

You could also get popping because you have a leak somewhere in your exhaust. Did you remove your old crush washers and add new ones when you changed out your pipes?
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Old 09-07-2008, 01:27 AM   #13
Lou
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The dynojet did come with a set of pilot jets.

I ran the bike with the pilot jets from the kit for several months with no success. When I contacted MAC, they suggested to go back to the stock pilot jet which I did.

In fact when I did that, some of the popping went away.

I did replace the crush washers when the pipes where replaced.

I'm a self taught curbside mechanic, so I really DONT know what I'm doing (in the technical sense), but I've been very thorough in each of my steps. I even replaced all the mounting studs on the block that secures the pipes to the engine to make sure it is seated correctly.

Problem is every time I take the bike to someone who "knows" what they are doing I end up back on the street fixing what they did wrong.

I'm trying not to take your comment personally, but I'm having little trouble with that.

I thought the point of this forum was to share knowledge with others like me who do their own work, but have no technical training as a mechanic.

I appreciate the response, and as a last resort, I'll take the advise to go to someone who can do a professional tuning, but before I go and give away $200 dollars, I would like to try and get it right myself.

When I read Shag's post, I thought that maybe the carbs are not the problem, maybe the problem is the pipes, if he resolved the problem, I would love to hear how he did it.....Shag, are you out there?????

Lou
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Old 09-07-2008, 04:22 PM   #14
lang
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Nah man, don't take it personally. You certainly didn't get any of the "fuckin' noob" shit from me that's common around here.

There's nothing wrong with knowing you don't know what you're doing. I'm just shadetree too - I learn by doing, watching, and reading. I often don't know what I'm doing.

My concern was that you were doing things to lean your mixture when I felt that it should be richened. That seemed to me like you didn't know what you were doing. You don't know me, I don't know you. You've posted again and I can see you've thought it through and tried a bunch of different shit. You're beyond my help now - I gave my meager advice and now I know it wasn't needed. But how many times have I heard someone say, "man there were no crush gaskets under my pipes so I just put in new ones" (a lot) - I didn't know where you were coming from.

The only reason I posted at all was because I'm thinkin you won't get a response from Shagman since he hasn't posted in 2 years and hardly anyone posts in the Classics section.

And as far as gettting dynotuned - I don't know why everone doesn't do this. You'll never get it dialed in perfectly because you don't have the machinery. A plug chop is all well and fine, but after buying pipes, a jet kit and filter, for a couple of extra bones get the motherfucker tuned right.
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Old 09-07-2008, 09:31 PM   #15
Lou
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Lang,

No worries man, I hear where you are coming from.

I'm not too thin skinned that I cant just get over stuff.

I do agree with you that a professional tuning would be great. Problem is that I have a wife. (period)

After the pipes, jetkit, and that new tank I bought this year, I will have to wait till next season to spend another big chunk of change.

Wait till she hears about the new risers and handlebar I want to get!!!!

Thanks for taking the time to post, I really appreciate it.

Lou
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Old 09-07-2008, 10:09 PM   #16
lang
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doesn't the jet kit come with a free run on the dyno? I've always thought it was a good idea to get it dialed in as close as I can and then go to the pros to check the work - if you've got the coupon, it's gravy.

Whatcha thinking about as far as risers? Dogbones? I've always wondered whether the top tree from an 86-88 would fit the first gen 83-85's - the 86-88's had removable risers so that would open up a world of options for you. I should actually have an extra 86 top tree in a month or so if you want to do some experimentation.
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Old 04-20-2009, 08:52 PM   #17
1987vt700
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I put the mac exhaust on my 87 Vt700 didn't re-jet...I did rebuild the carbs though. But I have been running the exhaust for 2 years and sounds great with no backfiring and plugs still look great!
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Old 12-20-2009, 08:00 PM   #18
Duffmyver
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I have the same backfiring on my Macs, Im running an 85-86 1100 and since I installed them its been backfiring when letting the throttle go.
Thanks for pointing me in the right direction with adjusting the carbs guys, I was pondering taking it to a shop to get em to do it but if all i gotta do is readjust the idle running im sure i can manage that.
I do take it this is still the same even though i aint running a dynokit right? (Uni airfilter going in soon, still considering the dynokit)
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Old 12-20-2009, 08:10 PM   #19
mcvierh
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Duffy....that isn't backfire, it's called decel pop, it comes from running to lean...enrichen the Air/Fuel mixture and it will go away....go to search and look up adjusting A/F mix....hundreds of posts on it.
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Old 12-20-2009, 09:45 PM   #20
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Ok cheers mate i will check out and gather some info thanks.
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