Topic: calling on the cb500/550 guys running 750 carbs

[Mitchell]

What are you guys running for carb intake insulators?  Ive got a set of sohc 650 boots now but they need to be turned around backwards to fit up and don't seem to make a good seal. Will the stock set of 550 boots work? I need to buy some but don't know which way to go, I don't have any 550 boots to try.

[kerryb]

Can you do that?  The 750 boots are too big to seal on the 550 intakes.  But they are close.  When is a carb too big for the cylinder it is trying to feed.  How would you get a smooth transition from carb to intake to reduce turbulence?
I was surprised that the spacing is darn close.  If you could get a good seal, you could try the carbs, but I'm gonna guess there would be some jet changes.  But don't take my word for it, I haven't got a clue!, just questions and carbs.

[ekpent]

 Is there some performance gain there ?  Seems like a lot of hassle and you would end up running with pods also.

[Mitchell]

Carbs are on the bike running and jetted  using 650 intake boots turned around backwards . when I was building the bike I used the 650 boots to get it all together and was planning on finding better fitting boots upon start up. Long story short i forgot about them and they worked well up until yesterday. I pulled her out the garage and fired her up and she was idileg up and down like it had a vacuum leak that's when I remembered I need to get better fitting boots. I loosend up the clamps and pushed the carbs back up tight and tightend the clamps back down and it runs fine again. I'm afraid the carbs are slowly slipping out of the boots because the carbs don't slip in to the 650 boots deep enough.

[Mitchell]

[FromBrowser]


I guess the performance gain would be 26mm throats verse the stock 22mm throats if my info is correct. Put it on the dyno over the summer and they claimed it made 53 horsepower, I ported the head and matched the intake runners, 650 cam, hooker 4-2 crossover exhaust , points with Dyna 5ohm coils, carbs have 115 mains with the needle one notch down from the top and foam pod filters.

[Steve_K]

With out an airbox, engine vibration could work the carbs loose.  Maybe, add support on the intake side of carbs to keep them in place.
Steve

[Mitchell]

That's a great idea steve , some support would most definitely help. After I read your post I went back out to the garage and noticed the carbs can be moved up and down quite easily, seems like that very well could be the issue.

[Mitchell]

Found this, looks like the cb500 boots work
   
http://forums.sohc4.net/index.php?topic=78430.0[FromBrowser]

Calj I will see if I can find the graph tomorrow and a pic of the plugs. I'm very skeptical of 53hp, I actually think I offended the guys running the dyno when I told them there was no way there dyno was right. Either way she's a pretty quick little scoot and runs like a sewing machine with the 750 carbs

[Mitchell]

Found this too, looks like the stock insulators will fit.
http://archives.sohc4.net/index.php?topic=12841.0[FromBrowser]