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BF 7.5hp running on 1 cylinder only at high speed transition.

D

Dognutz

New member
Hello,
I have had several issues with this motor previously and members helped me solve the problems, so many thanks and here's the next issue.
This is a 1978 BF 7.5hp motor with long shaft.
I got the motor running really well at low speed both cylinders fire and engine runs strong. When the motor transitions to high speed one of the cylinders doesn't fire and it runs rough. I took it to a shop they say compression is good and put in new points but can't fix the problem. They have been working directly with Honda and can't figure it out. When I first brought it in to the shop they said this is a great little motor and is in really good condition. Previous issues were out of time (so badly it wouldn't start), leaking oil fill tube seal, carb clean needed (I put on a brand new one, problem existed before and after), and needed points.
Thanks in advance,
 
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The first things i`d replace would be the condenser and spark plug for the cylinder that`s breaking down. If that doesn`t have an effect then the next thing would be to replace the HT coil feeding the effected cylinder. Any of these parts can seem to work fine at slow speeds but can break down as the revs are increased.

It`s been a long time since i worked on motorbikes that used points setup but that`s certainly the way we used to do it when i ran my own workshop.

Matt.
 
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I think there is one set of points and one condenser.---Fires both cylinders at the same time.-----------Has valve clearance been checked ?
 
racerone said:
I think there is one set of points and one condenser.---Fires both cylinders at the same time.-----------Has valve clearance been checked ?
Click to expand...

I still need to pick up the motor and talk with the guy who worked on it. The information I had was passed along by the owner, apparently the mechanic doesn't do phone conversations? I will update once I get the motor and check your suggestions.
Thanks,
 
Hi,

Looking at purchasing a BF20 motor, the seller is not sure how old it is. The number he gave me is,

BAMJ103013? (I cannot read the last digit in the photo supplied, if it is needed to determine age I can get back to him).

Besides the manufacturing date does the code give any other information.

Thanks to anyone who can help,
 
I picked up the motor. It has a Siamese coil both spark plug wires come out of the coil. I had the plugs replaced and the points cleaned and set. I even replaced the coil. the problem still exists. If I ease up the throttle I can get it to run great then it hits some point and breaks up then I have to back it down and start over. If I throttle up quickly it breaks up right away.
 
You must do this test !--------See if the spark will jump a gap of say 3/8" or more.------Maybe it is the primary coil under the flywheel that is at fault.
 
Hello,I have had several issues with this motor previously and members helped me solve the problems, so many thanks and here's the next issue.This is a 1978 BF 7.5hp motor with long shaft.I got the motor running really well at low speed both cylinders fire and engine runs strong. When the motor transitions to high speed one of the cylinders doesn't fire and it runs rough. I took it to a shop they say compression is good and put in new points but can't fix the problem. They have been working directly with Honda and can't figure it out. When I first brought it in to the shop they said this is a great little motor and is in really good condition. Previous issues were out of time (so badly it wouldn't start), leaking oil fill tube seal, carb clean needed (I put on a brand new one, problem existed before and after), and needed points.Thanks in advance,_________________________ladies leather jackets ladies leather jackets hand bags 4 sure hand bags 4 sure learn spanish learn spanish mcat practice test mcat practice test
 
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