135 carbs on 115 crossflow

[Indymike]

Hello all.<br />What can I expect (good or bad) by replacing the carbs on my 1973 115 Johnson with carbs for a 1975 135. I came across a deal on a set of new old stock carbs. The original carbs on my motor are somewhat worn at the throttle shaft bushings and seem to hang up the throttle plates a little when throttling back to idle, causing it to idle too fast. Both the original carbs and the new ones are 1-5/16" bores. What about jetting ? I would replace gaskets seals and floats before putting the new carbs into service. <br /><br />Thanks for looking,<br />Mike

 

[javsam]

Re: 135 carbs on 115 crossflow

well,make sure the jets are the same sizes.its worth a try.<br />javsam

 

[Dhadley]

Re: 135 carbs on 115 crossflow

The jets will probably be different in the two carbs. Use each set as produced. DO NOT change them. <br /><br />Unless youre set up is perfect you'll probably see a slight decrease in holeshot and slightly more fuel consumption. You may see a slight increase in top rpm. Maybe not.

 

[gatorred]

Re: 135 carbs on 115 crossflow

the size of carb is set if your 115 is bored to over size where the old carb's are worn out or under size then check the plug's for color and keep them from running to rich, tan to white is color I look for just a though

 

[WillyBWright]

Re: 135 carbs on 115 crossflow

Look down the throats of the carbs including the ID of the venturis. If the ones from the 135 are larger, you might get a bit more power. But remember, 115s are the largest Hp crossflows and 135s are not the largest Hp loopers. The 115 carbs may well be larger than the 135's.

 

[Walker]

Re: 135 carbs on 115 crossflow

There are 140 crossflows and the 135 is a crossflow not a looper.

 

[Indymike]

Re: 135 carbs on 115 crossflow

Thanks guys.<br /> The carbs do have different high speed jetting from the new (61C) to old(67C).Both idle jets are 30. I am running boyesen reeds and bumped the originals to 32. Do I bump up the size of the new idle jets to 32 as well?

Unless youre set up is perfect you'll probably see a slight decrease in holeshot and slightly more fuel consumption. You may see a slight increase in top rpm. Maybe not.

Holeshot now is pretty good. But I do need to get the revs up.<br /><br />Should I hunt up a bubble back for the exhaust?<br /><br />(EDIT: added the jet sizes.)

 

[jimmbo]

Re: 135 carbs on 115 crossflow

If I remember correctly, the 115s and the 135s and most of the 140 crossflow used the same size carbs. A few 140s in 77 ans maybe 78 used a slightly larger carb. Different jets don' tell the whole story as the carbs air bleeds can be different too. As for a 135hp looper? There was one made a couple of years ago but not to worry, the carbs on a looper will not mount on a crossflow and versa-vice.<br />Bubbleback is what gave the 99.6cu.in. block the increase from 115 to 135 or 140hp. correspoding stuffers need to be added to the exhaust chamber of the block. That will require some machining to fit. Also the exhaust tube(megaphone) is differnent, the best one is from a 1977 140hp.

 

[Dhadley]

Re: 135 carbs on 115 crossflow

The high speed jets stay with the carbs that they came in. You may have to fool around with the idle jets to compensate for todays fuel, engine height (backpressure) at idle, worn carb shafts etc.<br /><br />Unless you were near 6000, or more, before the carb change I doubt youll see much. The 115 carbs will carry the motor well beyond 6K.