K&B 3.5 problems

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K&B 3.5 problems

Postby cdxanti » Thu Jul 22, 2010 6:51 pm

I was given a 3.5 awhile back and I have never been able to get it to run.
The engine puts out no backpressure. So no fuel is being delivered. I believe it has the wrong exhaust adapter on it. Their is a gap between the head and the adapter that looks like is supposed to be their. I'm open to any suggestions.
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Postby SteveM » Fri Jul 23, 2010 3:22 am

Is this an inboard or outboard motor?
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Postby cdxanti » Fri Jul 23, 2010 12:43 pm

outboard
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Postby SteveM » Fri Jul 23, 2010 1:31 pm

Is the header perhaps an after market type designed for an exhaust throttle? Can ypu post a picture?
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Postby cdxanti » Sat Jul 24, 2010 8:22 am

Image
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Postby SteveM » Sat Jul 24, 2010 11:32 am

Looks to me like you have the header designed for the exhaust throttle for sure. You'll need to replace that with a new stock one. The red carb is from the older 7.5cc inboard motor and is a PITA to tune on a stock 2.5 outboard. I'd recommend the black or gold carbs instead.
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Postby cdxanti » Sat Jul 24, 2010 8:53 pm

so getting the right adapter would help with my back pressure problem?
Also I have another lower end that doesn't have a pressure fitting at all and is shorter than the one shown in my photo. is this for the exhaust throttle control?
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Postby SteveM » Sun Jul 25, 2010 3:15 am

cdxanti wrote:so getting the right adapter would help with my back pressure problem?
Also I have another lower end that doesn't have a pressure fitting at all and is shorter than the one shown in my photo. is this for the exhaust throttle control?


The lower unit with the short skeg is an older version. There wasn't a lower unit specifically designed for the exhaust throttle. The exhaust throttle kits were sold by Prather and provided the instructions on how to modify the stock lower unit.

The stock adapter will help with the back pressure for sure.
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Postby mrmodify » Sun Jul 25, 2010 6:15 pm

Have a 3.5 outboard had trouble with it for years. It never would run a 6oz tank dry. Some of the time it wiould make 2 -3 laps on pond then die. Most of the time it would go about 40' and die. Changed all kind of parts with no luck. Talked to Conley engines and was gonna put a Perry fuel pump on it. Conley talked me into putting a Perry carb on it. The boat now will run the 6oz tank dry at any speed you want as many times as you want..
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carb needle

Postby lobofeind » Sat Oct 30, 2010 5:36 pm

I have a h&b 7.5 outboard and the carb has no high speed needle.
Does anyone know were I can find one or one from another model that would work.
This engine is on a beautiful old dumas hull and i would dearly like to run it.
Thanks for your time.
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