Author Topic: Troubleshoot this!! (Read 3726 times)

TomL · « **on:** June 02, 2009, 05:02:25 PM »

1973 350f: rebuilt, cleaned carbs. New air filter (stock type) with air box. Mac 4-1 exhaust. Stock size jets and needles etc. Adjusted timing. New plugs.

My question: Bike revs freely and runs great up to about 5-6,000 rpms. Then it hits a brick wall and doesn't want to rev higher. These puppies are supposed to make a lot more power in higher revs. So. What's wrong? Jets? Carb sync?

Oh and one other thing. My front brake drags and it has been squeaking which is pretty annoying. I rebuilt the master cylinder and popped the caliper apart and cleaned it. I tried adjusting the caliper bracket to make more clearance but it didn't help much.

Help as always is appreciated. You guys are great.

Old Scrambler · « **Reply #1 on:** June 02, 2009, 05:23:52 PM »

I have a friend with a 350F but am not directly familiar with them. Is the stock baffle in the pipe? Try one size larger on the jets and be sure your air-filter is flowing. The brake will have some drag but the disk should not get hot. Since you just cleaned the caliper, I would put a few miles on the bike with ordinary braking to see if it improves. If the disk gets hot you have a sticky puck. Clean the caliper body and the puck but don't remove any metal.

mattcb350f · « **Reply #2 on:** June 02, 2009, 06:29:15 PM »

My 350F has stock jetting and the MAC 4-1 and runs well enough....

...I suspect ignition. Check the points again, and pay attention to the springs. Weak/broken springs could cause this.....or gap and timing for that matter.

Also make sure the little intake on the airbox is clear.

Make certain all the regular tune-up issues have been covered before changing jetting. It should run up to the redline with stock jets.

Matt.

HondanutRider · « **Reply #3 on:** June 02, 2009, 06:35:12 PM »

Ditto on the timing, as Matt says. Check and adjust your point settings.

Steve F · « **Reply #4 on:** June 02, 2009, 06:45:02 PM »

Make sure that the advancer is not stuck.

TomL · « **Reply #5 on:** June 02, 2009, 07:22:40 PM »

I have already adjusted the points and gaps. Timing also advanced alright. I did notice when I was timing it, that one of the points would occasionally have a visible spark. There are stock baffles in the MAC. After adjusting the timing, I got a smoother running engine that idled better, but not any higher revving. More ideas please.

TomL · « **Reply #6 on:** June 02, 2009, 07:29:18 PM »

Little intake on the airbox???

patrickd · « **Reply #7 on:** June 02, 2009, 07:31:20 PM »

Try reducing the point gap by 1000th" and see if it will rev higher. If the gap is too big they can't get closed fast enough at those high rpms

TomL · « **Reply #8 on:** June 02, 2009, 07:33:57 PM »

Worth a try i suppose. I gapped it according to the manual but it's a simple thing to try.

TomL · « **Reply #9 on:** June 03, 2009, 08:06:14 PM »

If anyone has any other things that would be a likely bet please throw them out there.

kghost · « **Reply #10 on:** June 03, 2009, 08:15:14 PM »

Fuel, Air, and Ignition.

Fuel..

Make sure your getting good flow and that the flow is unobstructed.

Make sure the float level is set right. Too low would cause what you describe.

Make sure the emulsion tubes under the main jets are clear.

Sync the carbs. If you have one way off its gonna be screwy.

Air.

Make sure the valves are set right and to spec. Cam chain too.

Make sure there are no obstructions to the airflow.

Filter in right? Lid on the filter?

Ignition the other guys covered....

HondaMan · « **Reply #11 on:** June 03, 2009, 09:56:23 PM »

Has the bike been sitting (dry) a long time? This can cause the orifices in the emulsifier tubes to partially close with a crusty material: it must be physically removed, will not dissolve out during cleaning. This can restrict fuel lift at upper midrange RPM.

The 350F should head for 10,500 RPM like it was hungry for it. They always did!

bender01 · « **Reply #12 on:** June 03, 2009, 10:09:25 PM »

Will it rev higher than 5-6k in the garage? Or only 5-6k when riding? Check float height. Do you have a fuel filter other than stock? Just checking!

TomL · « **Reply #13 on:** June 04, 2009, 08:44:56 AM »

I have completely disassembled the carbs. Separated them, replaced all hoses, including the ones between 1/2 and 3/4. Cleaned all crusty leftover gas. Took forever. Bike was sitting for 10 years. Adjusted timing, and cam chain as per manual. Wasn't able to adjust tappets. No loud ticking. The engine will rev over 6,000 in neutral or on the center stand. Just not while riding/under load. Still needs a sync but I don't want to have it done more than once. No gauges

. New stock filter in there with cover on. I set the float heights to stock. I think it was 21 or 22 mm. Only intank stock filter.

Seems to be the same problem this guy is having.

http://forums.sohc4.net/index.php?topic=52519.0

bender01 · « **Reply #14 on:** June 04, 2009, 09:12:05 AM »

Ive heard if the valves are too tight they wont wind up . It takes a special tappet tool to adjust the 350f. Or create one.

kghost · « **Reply #15 on:** June 04, 2009, 10:39:16 AM »

Quote from: bender01 on June 04, 2009, 09:12:05 AM

Ive heard if the valves are too tight they wont wind up . It takes a special tappet tool to adjust the 350f. Or create one.

Huh? I've never used a special tool....

TomL · « **Reply #16 on:** June 04, 2009, 04:55:51 PM »

So I stopped worrying about breaking it today and I just cranked on the throttle. After about 5-6000, it gets another burst of power. At around 8 it howls. Starts sputtering at that point. I really need to roll it on slowly too.

So I plan on raising the needles one notch. Maybe that'll fix the 5,000 rpm wall. Anyone know if that will help the 7-10,000 rpm range be any smoother? Does a carb sync smooth out top end as well as idle? Would that also alleviate some of my problems?

Regardless, I'm gonna swallow my pride and take the carbs apart again to move the needles and see what happens. Unless someone can tell me definitely it won't make a difference.

MJL · « **Reply #17 on:** June 04, 2009, 05:29:19 PM »

Quote from: TomL on June 02, 2009, 07:29:18 PM

Little intake on the airbox???

This. 650s are known to have the same issue, new pipes and the bike won't go over 60. Take the airbox cover off and go for a spin, see if it helps.

mattcb350f · « **Reply #18 on:** June 04, 2009, 06:16:15 PM »

Quote from: bender01 on June 04, 2009, 09:12:05 AM

Ive heard if the valves are too tight they wont wind up . It takes a special tappet tool to adjust the 350f. Or create one.

Yup. If it's been sitting for 10 years a valve adjustment it nessesary. it also seems like valve adjustment is all you've got left ....unless it's got a compression issue (stuck rings) $:-\$

Matt.

Mdub · « **Reply #19 on:** June 04, 2009, 06:56:02 PM »

Rather than take it apart, you can replace the main jets easily.
I just bought some 115's for 4 bucks apiece.

bender01 · « **Reply #20 on:** June 04, 2009, 08:05:01 PM »

http://www.z1enterprises.com/detail.aspx?ID=2870
this is the tool i bought.

Quote from: kghost on April 21, 2009, 12:08:49 PM

Motion pro sells a set if you have to have a store bought one.....

So what do/did you use? Needle nose and a wrench? I hate having tools I dont need.

HondaMan · « **Reply #21 on:** June 04, 2009, 08:25:03 PM »

Quote from: TomL on June 04, 2009, 04:55:51 PM

So I stopped worrying about breaking it today and I just cranked on the throttle. After about 5-6000, it gets another burst of power. At around 8 it howls. Starts sputtering at that point. I really need to roll it on slowly too.

So I plan on raising the needles one notch. Maybe that'll fix the 5,000 rpm wall. Anyone know if that will help the 7-10,000 rpm range be any smoother? Does a carb sync smooth out top end as well as idle? Would that also alleviate some of my problems?

Regardless, I'm gonna swallow my pride and take the carbs apart again to move the needles and see what happens. Unless someone can tell me definitely it won't make a difference.

This almost sounds too rich in the upper midrange. Lowering the needles would help, then. A side bet: Keyster needles may have been installed in the carbs. Check them when you take it apart: if they are not genuine Honda needles and jets, my advice would be to get some...

A carb sync is for the lower 1/3 of the throttle range. It is intended to smooth out irregularities in the intake ports so as to make the engine tractable. Above 3500 RPM, it has no appreciable effect in these engines.

Soos · « **Reply #22 on:** June 04, 2009, 10:36:52 PM »

First I would check valve clearances before moving your jet needle position.
Are all 4 pipes hot?

A bike sitting for 10 years might simply mean that it ran when parked, but needed a tuneup when parked too.
Add on 10 years of sitting, and you REALLY need to check EVERYTHING, while giving a good tuneup.

l8r

TomL · « **Reply #23 on:** June 05, 2009, 12:12:00 PM »

Why would Keyster needles not work? They can't be so different that they can't be adjusted to work right. All 4 pipes do get hot. At first they didn't. I cleaned the carbs again and got all four cyinders burning.

Setting valve clearances would involve finding special feeler gauges that would fit into tappet hole and getting a tappet tool or finding something that would work. How would valve clearance change from sitting? Better yet, how would valve clearance ever change? Same valves, same engine. It doesn't seem like the clearance would change on it's own. Could valve clearance problems really cause what I am observing?

Honest questions here. Not being a jerk. Thanks for the help.

HondaMan · « **Reply #24 on:** June 05, 2009, 04:23:32 PM »

Quote from: TomL on June 05, 2009, 12:12:00 PM

Why would Keyster needles not work? They can't be so different that they can't be adjusted to work right. All 4 pipes do get hot. At first they didn't. I cleaned the carbs again and got all four cyinders burning.

Setting valve clearances would involve finding special feeler gauges that would fit into tappet hole and getting a tappet tool or finding something that would work. How would valve clearance change from sitting? Better yet, how would valve clearance ever change? Same valves, same engine. It doesn't seem like the clearance would change on it's own. Could valve clearance problems really cause what I am observing?

Honest questions here. Not being a jerk. Thanks for the help.

I'm just recommending that you might check the needles, here's why:

The Keyster needles in the 500/550/750 carbs have a real bad track record of being the wrong tapers. Some SOHC4 users have even reported getting different tapers and differing lengths with the same part numbers when buying sets of 4 for these bikes. I've even seen pix here at SOHC4 of the same story with their fuel valves and seats, in a set of four.

I just finished a month-long e-mail troubleshoot with one of our members on a 550, trying to rectify a real severe stumble at about the same RPM range you're fighting: I completely forgot to ask him to check for Keyster needles. After trying every adjustment possible, to no great success, he discovered they were Keyster and bought Honda: problem solved in two hours. Search the forums for Keyster and you'll find lots of similar examples. They may work on other carbs, but have a poor history on the SOHC4 sets.

I don't wish to be "down" on any particular parts builder, if they are trying to make stuff for our toys. But, I don't know anyone at Keyster, or else I would pursue the fix with them, as an Engineer. I've done this already with a couple of our non-Honda 'suppliers', and they have been eager to fix the problems: very promising for our future! So, if anyone who reads this thread does have a clue to a Keyster contact, please forward to me?

News:

Author Topic: Troubleshoot this!! (Read 3726 times)

patrickd