Carburetor

[Lubosleftboot]

I would like to know the difference in the carburators between the Jonny 7.5 and Jonny 5 hp....Is it just a main jet size or is the carburator totally different?as in throttle body size,slide size etc?

Both motors are 164cc so it would seem to me that power output regulation would be achieved by using a restricted carburator to strangle the power from the same power head...but I am by no means certain.The engines I refer to are mid 1980s models...

All advice appreciated...

LLB

 

[JB]

Re: Carburetor

It is definitely NOT jet size, LLB. That is a myth that has been around since the 50s, at least.

Manufacturers don't tell us (won't is more like it) about differences in carb throat size, reeds and reed plates, port timing, compression ratio, exhaust geometry or tuning specs. Those are usually the things that are different in name brand engines of same displacement and different rated HP. Those are the things I changed in 2 stroke engines for kart racing to get high HP, short lived engines.

It is true that some manufacturers use restrictor plates and retarded ignition specs to detune some models, but I never heard of OMC doing that.

 

[Lubosleftboot]

Re: Carburetor

Thanks for the reply AM but in motorcycles restriction is usually done either through the carb or the port size...the port size route is more expensive as different tooling is required at the manufacturing stage..where as the carb can be modified without such tooling expense by either have a larger throat carb or indeed an adjustable main jet as is common in SU type carburators found on 1980s british built cars...

Could you point me to any websites devoted to the OMC motors as I would like to get to the bottom of this...

TY LLB

 

[Lubosleftboot]

Re: Carburetor

Hi AM

Just had a look on the BRP parts site and the intake manifolds are removable and appear to be different sizes between the 6 and 8 hp motors....this would restrict the flow of gas and therefore power what do you reckon?

LLB

 

[F_R]

Re: Carburetor

Lubo, you can go the BRP parts site and do the legwork yourself. If the part numbers are different, the parts are different. I haven't looked, but it's a pretty safe bet that the carbs are different venturii size. No, you can't just change the jet, that will just screw up the mixture. Copy and paste this without the quotation marks "http://epc.brp.com/default.aspx?brands=ej&lang=E"

 

[Lubosleftboot]

Re: Carburetor

Lubo, you can go the BRP parts site and do the legwork yourself. If the part numbers are different, the parts are different. I haven't looked, but it's a pretty safe bet that the carbs are different venturii size. No, you can't just change the jet, that will just screw up the mixture. Copy and paste this without the quotation marks "http://epc.brp.com/default.aspx?brands=ej&lang=E"

Hi F_R

Thanks for the reply but I cannot get anything to come up on my screen with that link.except for an empty box and a brp insignia....Cheers all the same

LLB