Author Topic: Carb woes, AKA Check your fuel level. (Read 4871 times)

Sticky Gerbil · « **on:** March 31, 2014, 05:49:47 AM »

I am having intermittent running problems-plugs appear rich- and have pulled my fuel bowls to find them dirty. What do I need to rebuild these dudes? I am a car mechanic.

Attached is a pic of my carb setup- was told they are 750 carbs.

Sticky Gerbil · « **Reply #1 on:** March 31, 2014, 06:33:43 AM »

Little more info:

So the bike ran great for a week. Just ten minutes ago, going up a hill it bogged down like it was about to die and had no power.

Full tank of premium. It sat over the weekend, today it is 33 degrees out. It ran fine for the 15 or so minute drive over here, which is a semi-trafficky ride (lots of stop and go). I parked it as I was at work anyway (lucky me), but I am wondering what the hell is going on.

Going up the hill, I put the choke on to see if it made a difference- the bike ran worse. I'm thinking this is a rich issue rather than a lean one. Maybe a needle is stuck open? Thoughts? Also, when not under load, bike is fine.

Sticky Gerbil · « **Reply #2 on:** March 31, 2014, 07:27:14 AM »

chirp chirp...

goldarrow · « **Reply #3 on:** March 31, 2014, 08:27:00 AM »

Looks like your bike is a Franken bike??? 650 motor, 750 carbs, and PODs. Would need trial and error than anything else in solving issues, IMO.

Sticky Gerbil · « **Reply #4 on:** March 31, 2014, 08:47:15 AM »

yes it is. Any idea which rebuild kit I need?

scunny · « **Reply #5 on:** March 31, 2014, 08:57:38 AM »

wouldn't worry about a rebuild kit yet. pull the carbs off and get all jets and passageways clean first.

madmtnmotors · « **Reply #6 on:** March 31, 2014, 09:12:24 AM »

Quote from: Sticky Gerbil on March 31, 2014, 07:27:14 AM

chirp chirp...

Really? After just an hour?

I've spent longer on hold with dedicated phone support more than once for various products. Most of the members here actually have a life outside of this forum...

Responses here can often take a day or more...

even in the SSDB!

http://forums.sohc4.net/index.php?topic=17422.msg1527897#msg1527897

atm cycles · « **Reply #7 on:** March 31, 2014, 09:14:27 AM »

By the look of those pipes I'd say it running lean

Sent from my iPhone using Tapatalk

goldarrow · « **Reply #8 on:** March 31, 2014, 09:14:48 AM »

Members get drunk in the SSDB and can't response or type...

goldarrow · « **Reply #9 on:** March 31, 2014, 09:16:48 AM »

Quote from: atm cycles on March 31, 2014, 09:14:27 AM

By the look of those pipes I'd say it running lean

Sent from my iPhone using Tapatalk

The fact that bike is Franken bike, pipes could previously come from other bikes.

madmtnmotors · « **Reply #10 on:** March 31, 2014, 09:38:54 AM »

Those pipes are a lovely shade of purple.

Like scunny says, check the carb floats and passages, and maybe read the plugs too. Make sure it hasn't leaned out for some reason.

Sticky Gerbil · « **Reply #11 on:** March 31, 2014, 09:52:38 AM »

Got the bike home with a mixture of choke and no choke. Had to push this pig the last 30 feet- I need to work out. Pulled the plugs- 1-rich, 2-lean, 3-rich, 4-lean. Pulled #4 carb bowl and pulled the float and two jets. The needle had an uneven seating pattern, and the bigger jet had rusty crap come out. Sprayed carb clean up into it, then decided I was being lazy and should just take the bastards off. Yes I have an inline FF. Yes I checked spark. Yes the tank is clean. No I don't have a pet cock.

I cleaned and regapped the plugs, then put them back in for now. Guess I'll pull the other bowls when I get home, but I need bowl gaskets anyway, so does anyone know which carbs these are? Also, if I remove them, will I need a sync tool when I go back with them? Again, I am a car mechanic- the most carbs at a time I have dealt with is 1.

madmtnmotors · « **Reply #12 on:** March 31, 2014, 10:32:10 AM »

Quote from: Sticky Gerbil on March 31, 2014, 09:52:38 AM

if I remove them, will I need a sync tool when I go back with them?

Bench synching is close enough to make it run. Sounds like fuel flow is the primary issue.

Pigford · « **Reply #13 on:** March 31, 2014, 10:45:35 AM »

Also be worth checking the ignition is healthy - make sure there's a good + 12v supply to the coils with the bike running

Sticky Gerbil · « **Reply #14 on:** March 31, 2014, 12:49:55 PM »

Spark is fine. Does anyone know what these carbs are?

lucky · « **Reply #15 on:** March 31, 2014, 01:02:56 PM »

A motorcycle carb is a lot different than a car carburator.

With the motorcycle the main concern is the float needle condition,
and the idle jet being kept clean.

Remember all other tune up items must be checked off before you work on the carbs.

DO not take the carbs all apart. It is not necessary.

You will need to tell the forum members what the main jet size is. The idle jet size and what position the clip is on for the slide needle.

You need to get some experienced help.
Those air filters are going to make your job of getting this bike running correctly
will be much,much harder.

The stock air filter box had a very small opening for the air, and the paper filter restricted the air flow too and acting as a choke .
So getting the carbs dialed in could be a REAL project.

If you are a beginner I would try to get the stock air filter if possible.
I do not know how it will fit.

Sticky Gerbil · « **Reply #16 on:** March 31, 2014, 01:08:02 PM »

So does anyone know which carbs these are? Can I at least get an answer as to how to tell?

harisuluv · « **Reply #17 on:** March 31, 2014, 01:13:09 PM »

you have cb750 carbs from somewhere between 71-76

Sticky Gerbil · « **Reply #18 on:** March 31, 2014, 01:19:52 PM »

Thanks.

Deltarider · « **Reply #19 on:** March 31, 2014, 01:51:36 PM »

Quote

and the paper filter restricted the air flow too and acting as a choke

.
Do you have any data that confirms your statement? No, you don't and your remark is nonsense. Why would a motorcycle manufacturer want the paper air filter to work as a choke?

Sticky Gerbil · « **Reply #20 on:** March 31, 2014, 02:49:01 PM »

Yeah, like I said I just wanted the carb type. Not same old tired ass lecture on air filters. That's why I ignored that statement.

seanbarney41 · « **Reply #21 on:** March 31, 2014, 06:22:06 PM »

Quote from: Sticky Gerbil on March 31, 2014, 02:49:01 PM

Yeah, like I said I just wanted the carb type. Not same old tired ass lecture on air filters. That's why I ignored that statement.

you need to understand this advice or you will remain a car mechanic always...but don't panic, if you can rebuild a quadrajet, you should have no problems with these, although they work wayyy different than what you are used to. they are much simpler but wayyy more precise and finicky. Fortunately, they often can be taken apart and put back together without replacing a single part. Don't bother with aftermarket rebuild kits. Just buy any o-rings that are damaged from Honda. If you think $10 is too much for a tiny o-ring, enjoy chasing your tail...Honda made subtle changes to these carbs at least once a year from 1971-1976. The casting number will help with some of the more specific details to a baseline to start tuning from. Casting number is found on this small pad between the number 4 carb body and the mounting plate looking down from the top...

harisuluv · « **Reply #22 on:** March 31, 2014, 06:38:53 PM »

Your welcome. And the debate vs pods/air filter mods and stock airbox will always be there.

In your situation, you should keep in mind you don't even have the proper carbs for your engine. There is not going to be much of a data set to look to for guidance. If I were you, I would trade those cb750 carbs to someone for 650 carbs. At least then you'll be in the ballpark.

Airborne 82nd · « **Reply #23 on:** March 31, 2014, 06:51:44 PM »

Sticky I am also new to these things so I started reading the FAQ and Tips & tricks sections and ran across this look at the casting# line then try to find one of those numbers on the carb bodies you have. I don't know where on the body but should be there some where then you might figure out what you have.

http://www.motorcycleproject.com/motorcycle/text/specs.html

Airborne 82nd · « **Reply #24 on:** March 31, 2014, 06:58:45 PM »

Quote from: harisuluv on March 31, 2014, 06:38:53 PM

Your welcome. And the debate vs pods/air filter mods and stock airbox will always be there.

In your situation, you should keep in mind you don't even have the proper carbs for your engine. There is not going to be much of a data set to look to for guidance. If I were you, I would trade those cb750 carbs to someone for 650 carbs. At least then you'll be in the ballpark.

Yes indeed plus 100% and it looks like you may be the man to trade with. Matching the correct carbs to the engine you have will save you a ton of hair pulling. In car terms thank of a six cylinder mustang with two 4s and ram air and no other mods stock engine

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Author Topic: Carb woes, AKA Check your fuel level. (Read 4871 times)