backfire

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rock42

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for all those that have been following me on my installation of coils etc, here is something new that i can't figure out. before going to a shop to see if they can get it going again, thought i would try here and let ya'll know what it is doing (or not doining). first i took it out for 150 mile ride and could not go over 70 mph and when climbing a hill could barely make it to the top. than just before arrive at home it was backfiring throught both exhaust pipes and barely got 30 mph. then all of a sudden stopped backfiring and ran at 65 mph and that all she would do. it just felt like it wasn't running on all cylinders, and then again later it seemed it was running smooth, but couldn't go faster that 70 mph and then it was struggling. any suggestions before it take it in to let professional get to it.
 

slabghost

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Sounds like it may be a combination of issues. Timing or stuck advance mechanism. Iffy connections to coils. Iffy plug wires. Plugged fuel filter or junk in the carbs. Might be plug gaps are too large. I'd check all of it. Add some cleaner to the fuel and do a tune up.
 

joedrum

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gee rock ...at one time my 79 was lik that it was all in the wires and ends plug ends that is you need to list everything thats been done .....i cant remember it all i remember the carbs are 1100 ....thats a plus ...idont remember the coils and such was it humid oraining during this funky running.... :mrgreen:
 

dan filipi

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Backfiring then running smooth makes me think crossfire on the wires first or points out of adjustment/pitted or timing off.
Not being able to get past 70 same thing maybe or carb/fuel delivery problems.
Each of these need to be ruled out to find the problem, I don't know of any other way except try the easy least expensive fixes first.
 

rock42

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reversed wires on coils they seem to be ok, reset gap on plugs am having trouble with wiring under the left side cover (battery side). will pull seat tomorrow and check wiring from ign to battery. also will check spark plug wires again been running sea foam and atf thru carbs. now noticed left front fork seal leaking and a rattle in the left tailpipe. if it not one thing it is another, glad i have my 99 shadow or i'd never be ridding this year.
 

rcmatt007

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are you sure you are getting enough fuel? try running it with the fuel cap off and see if that helps. While your description is breif, it almost sounds like afuel starvation at speed. But, then again, could easily be any one of the other problems mentioned. It never urts to clean up any and all 30+ yo old electrical connections
 

rock42

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will check with gas cap off and look at the exahust baffles. lucky i have a couple of spare exhaust in storage and can replace the old ones. am pulling off seat and checking some of the wiring that goes from ign to battery am having a problem with it. keeps shorting and keeping me from starting it without shaking the wires under the left side cover. will keep all of you posted and want to thank all for your help. will check each item suggested and the carbs will be last thing to check.
 

rock42

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ok ya'll i've checked most everthing else requimende by all and just finished pulling off the mufflers and the rattle in it (i think) was rust coming loose inside. started the wing with just headers and it sounded good and idle good, so here is my question i would like to replace not only the mufflers but also the headers as the left header (where the mufflers goes on) has been broken on and is inside of the muffler pipe. what i am wondering is my engine is a 79 while the bike itself is a 75 will a header and muffler from a 75 work on the bike, if not as we don't always have the money where is a good place to get a reasonable priced system without having to rejet carbs and not going to ebay?
 

rcmatt007

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the only thing that changed was the mounting points for the exhaust 75-79, but the exhaust ports are the same on every engine.

You do not need to rejet carbs changing out the exhaust, they are tolerant to LOTS of changes.

You have several options.
1: Try to find a set off fleabay (but remember any set you get will be over 30 years old and good ones demand a premium, and an ebay picture will not help you seperate the good from the cr%p)

2: Motad stainless set.... very $$$$$$ but top notch

3: are your headers okay? if so (or get some off fleabay) you have several options.

a: Jardine muffler sets (decent quality 3 ben range).

b: Some slip on aftermarket muffler (will take some modifying of brackets, but doable)

c: fleabay brand new HD mufflers (a sportster is your best bet) great quality, cheap price, but you will have to figure brackets to mount
 

rock42

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thanks will check things out i have a bad header on the right side, but had spare sets headers and mufflers on a 76 parts bike that looks very good. will jack them up and check and see how good they are.
 

rock42

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sounds like it might work, i am going to have to get a header for the right side or take it off and have some wielding done not sure which i am going to do. are those 1100's in pretty good shape?
 

rock42

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the end of the header where the muffler goes onto the header is broke off and is inside of muffler. going to try to pull it out and get it wielded or pull header off spare bike.
 

dan filipi

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If the pipes are in otherwise pretty good condition they could be welded back up.
Doing so ruins the chrome in that area so they'd have to be painted at least where the welds were done.

This is what I did.
I'm NOT skilled at mig welding by any means. In fact I had just bought a mig welder from Harbor Freight.
I first dug out the rust then tacked on a blank metal 4x4 electrical box cover.
Since the cover is flat, after tacking I hammered it down against the muffler to wrap it around, tacked and hammered some more til it was flat wrapped nicely then welded it on moving the wire weld quickly to keep from blowing through the thin muffler wall, which did happen many times but continued to fill.

Then I qround the welds down and shaped it to the contour of the muffler.

I'll post a pic, it turned out pretty damn good surprised me I actually pulled it off.
 
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