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Discussion Starter #1
Hey Geeto, thx for that tire info, those venoms look BADASS! About the choke, I only need it for a couple secs, I turn it off and she revvvvvs like hell then just dies...Is it possible that the points coulda come out of sync by kickstarting the hell outta the bike. I'm tryin to think what has changed since I got it, not much, but it was running perfect when I got her. There was one or two days that I was tryin to kickstart her like crazy cause the battery when kinda dead....Let me know dude-and I owe ya a drink...

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'73 CB350(RIP)
'74 CB750K3 Cafe Thriller

Edited by - wildcatmahone on Jul 18 2007 01:44:54 AM

Edited by - wildcatmahone on Jul 18 2007 01:46:50 AM
 

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points should not "come loose" from kickstarting the crap out of it. They can come loose if the bike gets knocked on it's left or right side. However points are a natural wear item and should be filed square, otherwise they are nod delivering optimal spark.

How are your carb boots? are they cracked at all. The only thing I can think of is that maybe you have a vaccum leak causing it to rev. Sure it would cause a lean condition but there is a chance something else is causing your plugs to foul.

Have you checked all plugs or just one? If you park your cb750 on its side stand for any length of time without running it the bike tends to foul the #1 plug. therefore it could be that 2,3,& 4 are lean and one looks fouled.
 

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Are you sure that the choke linkage is working properly? Just because you are pushing the cable in, are the chokes on the carbs turning off?

Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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Discussion Starter #4
Ok I'll definetly check my points..gotta find where to get a timing light. My carb boots are tight as hell, and my choke valve seems pretty tight. Yess it is all 4 plugs that were fouling up until I turned all my idle air screws 1/2 turn above factory spec, cleaned all plugs, and ran it again to discover the second one to the right of the shift lever side
(no.2?) was okay though the other 3 were fouled again...I am pretty convinced I am running too rich...

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the stock airbleed settings should be 1 and 1/4 turn out. Bottom out the screw and then back it out 1 and 1/4 turn. that should get you close but you will need to synch the carbs to get them just right (and if you don't have the tool you need to go to a shop).

I was thinking about something else yesterday, check to make sure none of your slides is sticking, that could be why the engine is racing when you shut the choke off.
 

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It revs like hell and then dies, and then you're looking at the plugs and wondering why they're fouled? Which problem are we trying to fix here? Because if that's what you mean to say, a perfectly tuned bike will have ugly plugs if you put the choke in, start it up cold, rev the shit out of it and then turn it off. SO, is the problem that it revs like hell after you take the choke off? Let's solve that one, because generally speaking, running rich doesn't make your bike rev like a bastard - the engine only burns as much fuel as it has air to mix with.

Check for air leaks around the manifolds at carbs and intakes. Check for a kinked throttle cable. Check to see that all slide pistons are returning to their happy homes on the low side of the venturi. Have you checked your choke linkage yet?

A
 

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i say F tuning four carbs, you should sell a kidney and get a set up like this

[

...connoisseur of slack...
the shot came from cyclexchange, from a occ type chopper built from a cb750. they built a tight bike (except maybe the exhaust) but the style still makes me want to barf

Edited by - snorkelfork on Jul 24 2007 02:04:31 AM
 

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Discussion Starter #8
So I was working on her all last weekend and looks like I've had a total breakthrough. From not even starting to running pretty smooth<img src=icon_smile_tongue.gif border=0 align=middle> Man that Clymer is my new best friend lol. You know I was just standing there scratching my head, wondering what the hell is wrong cause everything on it looks sweet. It would start right up with the choke then just die and foul all my plugs (and I felt like breaking shit). I eventually found out that I had to tune my idle circuit which after many hours and plug filing I did...Just messed around with the throttle stop screw and the idle air screws and that was it. There was just one problem...I couldn't get her to idle below 3000rpm without dying. After riding around for about a half an hour she started calming down a bit now she's idling at about 1200rpm.....Just wanna say thx to everyone for their advice. So what exactly is the correct procedure for tuning these carbs, reckon I should know the right way for next time(and I know their will be one)!

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Discussion Starter #9
Hey Snorkel whatsup yeh I actually discovered these revamped carbs the other day while surfing around....http://www.cyclexchange.net/Carb System Comp Page.htm
Any of you guys got anything good or bad to say about these carbs...? Looks like a sweet upgrade to have.

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they are ok for a stock bike, a little better than the stock carbs but that may be because mukuni VM carbs are just better overall. they don't really fit inside a stock frame without some mods and custom air cleaners. they do look sick however.

If you really want to get the most out of your CB you can buy the CR carbs cycle exchange also sells, which are only $100 more than the dual mukuni setup they sell and are way, way, way better. The fastest cb750s I have ever rode all had CRs or FCR carbs.

www.cyclexchange.net
 

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Discussion Starter #12
Does anyone have a good procedure for tuning Kei-chin carbs on a CB750?

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So on that first link it says


"
The "Main Jet" should be should be check for scaring, wear and corrosion, as all the parts....and needs to be sized as the factory suggests unless modifications in the intake (air filters), valves, cam or exhaust. Some of the later model CBs will convert from the air-box to single pod filters without changing jets, but almost always it IS necessary to get bigger main jets when going from 4x4 exhaust to a 4x1 header."

Ive got pod filters and a 4-1 with the stock jets, should i get bigger main jets? Where would i get them anyway?


My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
 

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So on that first link it says


"
The "Main Jet" should be should be check for scaring, wear and corrosion, as all the parts....and needs to be sized as the factory suggests unless modifications in the intake (air filters), valves, cam or exhaust. Some of the later model CBs will convert from the air-box to single pod filters without changing jets, but almost always it IS necessary to get bigger main jets when going from 4x4 exhaust to a 4x1 header."

Ive got pod filters and a 4-1 with the stock jets, should i get bigger main jets? Where would i get them anyway?


My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
 

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quote:
So on that first link it says


"
The "Main Jet" should be should be check for scaring, wear and corrosion, as all the parts....and needs to be sized as the factory suggests unless modifications in the intake (air filters), valves, cam or exhaust. Some of the later model CBs will convert from the air-box to single pod filters without changing jets, but almost always it IS necessary to get bigger main jets when going from 4x4 exhaust to a 4x1 header."

Ive got pod filters and a 4-1 with the stock jets, should i get bigger main jets? Where would i get them anyway?


My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
it is probably a good idea to get bigger mains. What do your plugs look like? have you done a plug chop test? What size are your jets now and how do you know they are stock?

does your bike stumble or surge?
 

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quote:
So on that first link it says


"
The "Main Jet" should be should be check for scaring, wear and corrosion, as all the parts....and needs to be sized as the factory suggests unless modifications in the intake (air filters), valves, cam or exhaust. Some of the later model CBs will convert from the air-box to single pod filters without changing jets, but almost always it IS necessary to get bigger main jets when going from 4x4 exhaust to a 4x1 header."

Ive got pod filters and a 4-1 with the stock jets, should i get bigger main jets? Where would i get them anyway?


My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
it is probably a good idea to get bigger mains. What do your plugs look like? have you done a plug chop test? What size are your jets now and how do you know they are stock?

does your bike stumble or surge?
 

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Discussion Starter #18
Yeh I gotta check my jets as well, too bad my bike started stumbling, my bike has got issues. I'm running pods and 4-1 exhaust too...here's some main jets on ebay, i guess the idea is to mess around with jet sizes and see what works best. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=018&sspagename=STRK:MEWA:IT&viewitem=&item=280131704438&rd=1
Screw these keihin carbs though I definetely am thinking about getting those revamped ones in the photo above, alot less of a headache. So how big of a jet is needed when running pods and a 4-1?

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'74 CB750K3 Cafe Thriller

Edited by - wildcatmahone on Aug 01 2007 02:18:31 AM
 

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Discussion Starter #19
Yeh I gotta check my jets as well, too bad my bike started stumbling, my bike has got issues. I'm running pods and 4-1 exhaust too...here's some main jets on ebay, i guess the idea is to mess around with jet sizes and see what works best. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=018&sspagename=STRK:MEWA:IT&viewitem=&item=280131704438&rd=1
Screw these keihin carbs though I definetely am thinking about getting those revamped ones in the photo above, alot less of a headache. So how big of a jet is needed when running pods and a 4-1?

Banned From The Pubs..
'73 CB350(RIP)
'74 CB750K3 Cafe Thriller

Edited by - wildcatmahone on Aug 01 2007 02:18:31 AM
 

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Discussion Starter #20
Anyway who wants a shitty stock airbox on their ride? It looks like a kitchen sink lol.

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