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i have a few questions about my 83 750. i took her out for the first time last week and she had a top speed of around 70mph :cry: ive read on here about checking the diaphrams on the carbs, still need to do that, what about jetting? i have a Uni air filter and what look to be Mac pipes, i dont think the prevoius owner rejetted. it has ok power at take off, but anything past half throttle it flattens out. i also have a little backfire at idle and deceleration. any info would be greatly appreciated. the local honda shop wants to charge me 90$ for a stage one jet kit but cant tell me what size jets are in the kit or what all it contains
 

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Since it does run, my first step would be a good fuel injection cleaner like Chevron. I believe the ratio is 1 oz. to 1 gallon of gas. Keep adding it until the whole bottle is used up. Also, you could try keeping the choke on a little.
 

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blake,

The Dynojet jet kit for your bike is #1101. The following link shows it'll cost you $65 plus shipping.

http://www.mawonline.com/dynojet.htm#Jet kits

The instruction sheet is usually available online at http://www.dynojet.com
but for some reason it's not available for this kit. It may be discontinued? Anyway, the instruction sheet comes with the kit and will recommend what to use for your particular set-up. The kit will have several sizes of main jets plus needles that are really the heart of the kit. The kit will have everything that you'll need to duplicate what their engineers determined to be the best set-up via their dyno-testing.

Brian
 

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blake1221 said:
i have a few questions about my 83 750. i took her out for the first time last week and she had a top speed of around 70mph :cry: ive read on here about checking the diaphrams on the carbs, still need to do that, what about jetting? i have a Uni air filter and what look to be Mac pipes, i dont think the prevoius owner rejetted. it has ok power at take off, but anything past half throttle it flattens out. i also have a little backfire at idle and deceleration. any info would be greatly appreciated. the local honda shop wants to charge me 90$ for a stage one jet kit but cant tell me what size jets are in the kit or what all it contains
A few questions:
When did the bike last run, prior to last week?

And, when it was running last (season or year or whatever) was it working fine then?

Or, has it gradually gotten worse and worse.


My first guess is that the jets are gunked up badly.
Carb cleaner really only maintains clean jets, if they are already clogged you pretty much need to pull and disassemble the carbs.
Take out the jets, blow them out with compressed air and clean with brake cleaner.
The holes through the jets are very very small, the smallest one is only large enough to pass a cat's whisker.
DO NOT try to stick narrow pieces of wire through the jets, it can scratch the inside and make the issue worse.
The cat's whisker is stiff enough to poke though the gunk, but soft enough to not damage anything.
You need one willing, or slow, cat for this item.

Guess #2: You have pinholes or tiny tears in the diaphragm(s).
If so, buy new slides/diaphragms from Service Honda.
They charge about $90 per part, everywhere else wants $140 or more.
You could try to buy some used carbs off ebay and salvage the slides from those, I've gone that route, but you have to remember that those parts are also over 20 years old and are probably ready to fail at anytime, if they haven't already.
Used carbs can be found for $30-$60 usually.
Like I said, I did that and salvaged the slides, but only got another couple months of riding in before those ones failed too; that's when I bit the bullet and bought the brand new ones from Service Honda.

Either way, you owe it to your wallet to figure out if either gunked jets or torn diaphragms are the problem before you take the bike to a mechanic.
They WILL charge you much more to fix it than it would cost you to do it, even considering your time outlay.

Good luck!
-K
 
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