Author Topic: cb350f rpms (Read 3542 times)

nealcuda1 · « **on:** March 21, 2009, 05:15:39 PM »

I have cb350f and I can't get it to rev over 5000 rpm. It just falls on it's face. The carbs have been cleaned and rebuilt, new plugs and points, the timing set. Any ideas?

mlinder · « **Reply #1 on:** March 21, 2009, 05:19:11 PM »

Have an air filter in there?
The smaller the engine, the larger the difference in performance with compromised AFR.

nealcuda1 · « **Reply #2 on:** March 21, 2009, 05:23:42 PM »

Yes I do but it is old but clean.

mlinder · « **Reply #3 on:** March 21, 2009, 05:40:12 PM »

Is the lid for the airfilter on?
Have you checked for leaks?

After that,

Are all 4 firing?
If they are, have you checked and adjusted your points?

nealcuda1 · « **Reply #4 on:** March 21, 2009, 05:51:18 PM »

The lid is on the air box. I just had new rings, cam and rockers installed. The carbs were set and the timing and points were set at a honda shop. This problem exhisted before the carbs were cleaned and the top end rebuilt.

mlinder · « **Reply #5 on:** March 21, 2009, 05:53:21 PM »

So...

Have you checked for carb boot leaks?

And are you capable of checking points and timing yourself?

nealcuda1 · « **Reply #6 on:** March 21, 2009, 05:56:29 PM »

no I haven't checked the boots for leaks. Yes I can set the points and timing. I owned a bike shop for 9 years but this thing has me stumped.

HondaMan · « **Reply #7 on:** March 21, 2009, 06:01:42 PM »

Check for a spark advancer that isn't advancing. This is common on the 500 and 350F that has been sitting a long time: sticky with old grease. Make sure the timing is advancing when revved, in other words.

Also: 2mm low on the float bowls will cause this trouble on the Baby Four: make sure of the float heights.

Finally: what exhaust pipes are you running? If not stock, they can lean out the AFR real quick, because this engine breathes like a day in fresh mountain air!

I sure hope to get one of these, one day...

mlinder · « **Reply #8 on:** March 21, 2009, 06:08:50 PM »

Quote from: HondaMan on March 21, 2009, 06:01:42 PM

Check for a spark advancer that isn't advancing. This is common on the 500 and 350F that has been sitting a long time: sticky with old grease. Make sure the timing is advancing when revved, in other words.

Also: 2mm low on the float bowls will cause this trouble on the Baby Four: make sure of the float heights.

Finally: what exhaust pipes are you running? If not stock, they can lean out the AFR real quick, because this engine breathes like a day in fresh mountain air!

I sure hope to get one of these, one day...

I'd give you mine, Mark, but I just gave it to prosolars girlfriend

nealcuda1 · « **Reply #9 on:** March 21, 2009, 06:17:25 PM »

What is the afr? I have 4 into 2 headers but I don't know the brand, I bought them used. The floats were set by wgcarbs of Texas.

mlinder · « **Reply #10 on:** March 21, 2009, 06:47:34 PM »

air fuel ratio.

Check the advance like Hondaman suggested. Then check float heights. Remember to check for airleaks too.

nealcuda1 · « **Reply #11 on:** March 21, 2009, 07:07:04 PM »

Thanks I will check these items tomorrow.

HondaMan · « **Reply #12 on:** March 21, 2009, 07:33:03 PM »

Quote from: mlinder on March 21, 2009, 06:08:50 PM

Quote from: HondaMan on March 21, 2009, 06:01:42 PM
Check for a spark advancer that isn't advancing. This is common on the 500 and 350F that has been sitting a long time: sticky with old grease. Make sure the timing is advancing when revved, in other words.

Also: 2mm low on the float bowls will cause this trouble on the Baby Four: make sure of the float heights.

Finally: what exhaust pipes are you running? If not stock, they can lean out the AFR real quick, because this engine breathes like a day in fresh mountain air!

I sure hope to get one of these, one day...

I'd give you mine, Mark, but I just gave it to prosolars girlfriend

RATS!

bender01 · « **Reply #13 on:** March 21, 2009, 07:36:11 PM »

These things are finicky. I cleaned my very bad carbs three times. The second to last it would revup fine until my 200lbs got on it. Third cleaning almost fixed it but the timing was tricky. I thought it was running good but it was almost lava hot after a 20 min ride. Timing light fixed that. Im running 75 jets and a mac 4>1. It carries me about 75-80 mph now(maybe faster if i tucked down) but I might get some 80 jets eventually. Im not lookin forward to taking the carbs off again . I also had starvation from not properly setting the floats. Also run it with out the air filter. That might be just old and broken down.(doubtful) Mines red so if yours is green or black than probably none of these tidbits will help.Got any pics?

tomkimberly · « **Reply #14 on:** March 21, 2009, 08:39:36 PM »

If you are a big man make sure when you sit on the seat the air intake does not get covered and closed off.

Tom

nealcuda1 · « **Reply #15 on:** March 22, 2009, 03:32:21 PM »

I took out the air cleaner and tried that, no luck. The only thing that helps a little is to run with the choke half on, it will rev to about 6500 rpm then falls on its nose.

fmctm1sw · « **Reply #16 on:** March 22, 2009, 05:28:28 PM »

How do your spark plugs look?

nealcuda1 · « **Reply #17 on:** March 22, 2009, 06:04:20 PM »

I don't know I will check them.

HondaMan · « **Reply #18 on:** March 22, 2009, 06:51:54 PM »

Quote from: nealcuda1 on March 22, 2009, 03:32:21 PM

I took out the air cleaner and tried that, no luck. The only thing that helps a little is to run with the choke half on, it will rev to about 6500 rpm then falls on its nose.

This symptom smacks of leaking hoses between the head and carbs, or low float levels.

HondanutRider · « **Reply #19 on:** March 23, 2009, 05:35:27 AM »

Besides all the good advise on what might be the problem, have you done the obvious? I often get confused and have to re-think which way turns on the choke and which way turns it off. Make sure it still isn't on.

flybox1 · « **Reply #20 on:** March 24, 2009, 08:07:53 AM »

i'm experiencing something similar on my 350F.
good acceleration to 5000 rpm, and then chugachugachugahh.
(50 mph max. yes, i'm a tall 225lbs, but i cant even pass grandma!)

all four are firing. 4 into 2 jardins
new batt, on float charger after every ride.
carbs squeaky clean. good fuel flow thru petcock.
boots sealed tight and no leaks.
filter is good. lid on tight. no air restriciton that i can see/hear.
new D8EA's, and lightly carboned at end of ride.
points done 2x. (@.014)
air screw out 3/4 turn (was at 1 turn out, but better mid rpm accelleration at 3/4 out)
air temps around 40-45F.

any way to check timing advance w/o timing light?

nealcuda1 · « **Reply #21 on:** March 24, 2009, 03:02:30 PM »

If I put the choke on I can get it to 6000rpm but that is as far as it will go. The whole top end has been rebuilt. This problem exsisted before I rebuilt it. New pionts, plugs, rings and all gaskets. I had the same problem with my cb200t and I cleaned out the main jets and that fixed it but on this 350f it has all new parts in the carbs. I put a inline fuel filter on it before I started it up.

mattcb350f · « **Reply #22 on:** March 24, 2009, 03:40:59 PM »

How's the fuel flowing out of the petcock? could be a clog up there.

Also check to make sure the tank is venting; there's a little hole on the underside which can clog up.

..at any rate, by the symptoms, it sounds like a lean condition.

Matt.

nealcuda1 · « **Reply #23 on:** March 24, 2009, 06:30:37 PM »

I ran it with the tank lid open and it didn't help. The advancer is working. The only thing now to try is installing larger main jets. This bike has set since 1992 but it ran great then. I know that was a long time ago but with everything I have done to it it should run now.

bender01 · « **Reply #24 on:** March 24, 2009, 06:38:39 PM »

Try taking the inline fuel filter off. The petcock screen should do the job. I ditched mine and it helped some. I think they have to be vertical to work properly. I did see a pic of a fuel line once that went down with a filter under the carbs and back up and over the right side. Dont know if it worked though. Are the valves to tight?

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Author Topic: cb350f rpms (Read 3542 times)