Topic: Honda 550 throttle hang

[Tweetip10]

First, thank you for the inputs to oil filter leak.  It would have saved a lot of time and money had I asked earlier.  Ok, next issue.  First, I installed a 4 into 1 aftermarket exhaust after my rebuild.  At first the rpm would hang about 2000 rpm then eventually drop to 1000 then die.  I read about adjusting the carbs from 2.5 turns on mixture down to 1 turn.  Bike will idle now but still hangs at about 2000 rpm.  If I lightly press down on the number 2 brass nut on carb linkage bike will go down to idle. Rev it, it will stick again.

[middletons]

My guess is that carbs are not synced, or the the idle mix is lean.

[Tweetip10]

They seem to be perfectly sync.  But maybe I need to switch gauges to see if they all agree! 4 gauge setup.

[ACK777]

Hello Tweetip10,

Try using the same gauge on all 4 of the carbs one after the other to see if they all agree and match.  Sometimes those things can start getting sketchy after a while and even though they all read the same they were never calibrated against each other so that is why I always sync with one gauge and then write it all down and compare and adjust from there.

[BenelliSEI]

+1 to Teetip10. Best practice is to connect all 4 gauges to one carb FIRST. Use a 5-6 barb hose connector and an extra short piece of tubing. Fire the bike up and adjust all 4 garages to read the same number. My Motion Pro unit instructions suggest doing this every time.

[Deltarider]

+1 to Teetip10. Best practice is to connect all 4 gauges to one carb FIRST. Use a 5-6 barb hose connector and an extra short piece of tubing. Fire the bike up and adjust all 4 garages to read the same number. My Motion Pro unit instructions suggest doing this every time.

BUT NOT SIMULTANEOUSLY!!

[goodtryer]

https://www.motionpro.com/a/syncpro-carb-tuner-08-0411/

It's part of the process with the MotionPro. Using the white plastic piece in the attached pic.

See the "Calibration and Use" section in the linked PDF.

[Deltarider]

If we talk gauges, meaning mechanical underpressure clocks, it cannot be done simultaneously, as the moving membranes will interfere. I once tried this with my set and judged the clocks were off. Took the set to where I had bought it and the man demonstrated with a stabil (non pulsating) vacuum pump, there was nothing wrong with them. So if you want to calibrate clock gauges, you'll need a non pulsating vacuum and certainly not a running cylinder.

[dave500]

if you have an old v8 car like me plug em all in to the vacuum advance port on the carb,itll be smooth and steady vacuum,a 6 will do aswell,im guessing some modern cars have a vacuum port somewhere you could tap in to?

[Tweetip10]

Ok, worked on carbs again today.  One gauge and swap lines.  Started on number one and read 8 in.  Set 2 to 8 in.  Set 3+4.  Went back to 1, now reading 3 in.  Adjusted to 8, checked 2, reading 3, set to 8.  Checked 3+4 now, reading 3 and adjusted. Still running bad and will suddenly drop to idle and die.  Kept Rpm was at 2000 whole time.  Just to see what adjustment I could get, I tightened 1 to max vacuum, 15 in, set 2 to 15, but number 3 would not go to 15, 4 to 15.  Gave up for the day.

[Scott S]

http://forums.sohc4.net/index.php/topic,184299.msg2133716.html#msg2133716

[dave500]

dont worry about the number they read,just get em all the same.

[craz1]

Its very hard to adjust all of them the same with just one gage. Adjusting one will affect the one you just adjusted. I would invest in a good digital unit and forget the gauges. They are not very accurate but should work ok as long as they are calibrated to one source. I use a mercury set up I made a long time back. The digital one is at a pretty good price point
https://thedigisync.com/product/the-digisync/

[Deltarider]

Maybe I have missed it, but who 'diagnosed' carbs needed to be synchronized? The fact is they rarely do. Below a page from the owner's manual.

[newday777]

First, thank you for the inputs to oil filter leak.  It would have saved a lot of time and money had I asked earlier.  Ok, next issue.  First, I installed a 4 into 1 aftermarket exhaust after my rebuild.  At first the rpm would hang about 2000 rpm then eventually drop to 1000 then die.  I read about adjusting the carbs from 2.5 turns on mixture down to 1 turn.  Bike will idle now but still hangs at about 2000 rpm.  If I lightly press down on the number 2 brass nut on carb linkage bike will go down to idle. Rev it, it will stick again.

Have you cleaned the carbs and linkages? If so how did you clean the carbs exactly?

Have you tested for vacuum leaks around the carbs and boots? What did you use to test?

Are you running pod filters?

[Tweetip10]

Okay, I sent carbs off to be professionally rebuilt. They were sync’d and adjusted for my std air box and 4 into 1.  Installed but had same issues.  Ran better but throttle hung if slowly brought rpm up to 2000 or above.  Throttle snap returned to idle sometimes.  Called rebuilder, he said spark advance sticking.  Removed, lubed, set timing, same problem.  Replaced advance with old one, same problem.  Removed electronic ignition replaced with new points and condenser, same problem.  Adjusted valves, same problem.  Removed spark advance, cut one spring 1/2 loop. Reinstalled set timing with previous mark.  Ran better when cool but as bike heated up rpm now stuck at 3000 rpm.  A note though, if you use the transmission to lower rpm below about 2500 now it will go to idle.

[Kevnz]

If you haven't read up the thread by Scott S, I recommend you do so. It's the most comprehensive description you will find, and it's dollars to doughnuts relevant to your scenario.

[dave500]

have they been vacuum synced on the bike yet?sounds like they were rebuilt and bench synced only?if they aint synced on the bike your chasing your tail.

[Tweetip10]

They were rebuilt and sycn’d by the rebuilder on a test engine with the same configuration as mine.

[Scott S]

http://forums.sohc4.net/index.php/topic,184299.msg2133716.html#msg2133716

 Have you read this yet?
 You're describing exactly what I went through.

 The answer is in that thread.

 Show us a picture of the sync screws and how many threads are showing.

[Deltarider]

The more talk about the syncing of the CB500/550 carbs, the more I'm tempted to give a link to that video, a member of the German forum has published. He had taken his CB500 carbs completely apart to the last and smallest possible parts, replaced some parts, galvanised others and then reassembled - step by step - gründlich explaining in the proces the function of everything and why he did what he did. It is there that I've learned how, most probably, carbs back in the day have been bench synced by Keihin before they were shipped as sets to the Honda assembly lines. The dilemma for me however is, his undertaking implies separating carbs from the rack and, quite honestly, I see no reason why you would ever want to do that. Some will argue: but I have to do that anyway, because I need to renew the o-rings at the T-joints. Question is: is it 'need to' or is it 'want to, now that you've bought a set of carb gaskets and you can't stand the feeling, that after spending the money, you will not use all of it '.
Don't get me wrong. There's always the possibility, they will leak some day, but so far my 45 year olds, don't, in spite of harsh treatment. There has been only one spring after that winter I had experimented with drained carbs, that there initially was a little leakage. A minute or so later, it had cured it self. I don't know if you're familiar with how much an already used gasket will shrink when left dry... but it is telling.
Honda did everything possible to eliminate carb maintenance as much as possible, like fitting two O-rings on each side of the T-joints. In spite of Honda's effort and its notification in the Owner's manual, what do we see in this forum?
I'm sorry but I feel responsible and will - as always - not send others into unnecessary 'repairs'.
I gave away my vac set, because I prefer a bench sync over standing in the noise and fumes, annoying my neighbours in the proces. I've proved myself that it can be done. More than once.
Prior to whatever method you prefer, it would not harm, to check the initial set up Honda did, is still there. Now, did Honda nothing wrong then? No, alas, Honda did: it's the error on p.8 of the Shop Manual CB500-550 that - probably for that reason - is missing in practical all copies I've seen on line. To learn more on this, go to:  http://forums.sohc4.net/index.php/topic,184299.msg2133957.html#msg2133957

[dave500]

they have to be synced on your engine full stop,the guys a #$%*witt saying they are now synced for your engine,they wont have the same compression or vacuum.

[bryanj]

Dave, when i was in a dealers i was trying to sync a set of v4 500 carbs and had to give up take them off the bike and sync with a drill. When refitted the vacs were well within spec

[dave500]

good fluke.

[Scott S]

 Delta, I totally get your point about "Why do all this", but only on bikes that have been in constant operation of some sorts.

 I, and many others, rescue bikes that may have sat longer than they were ridden.  The rubber is degraded, the gas has degraded, the aluminum has corroded,  etc.
 When they are at that point, a full and complete disassembly is required.

 You ARE correct about the proper reassembly,  and I...and hopefully others here...have learned about the proper way to do this.
 And once you've gone that far apart,  and back together again, a bench sync is a MUST, and a vacuum sync is better.
 I've personally seen the improvements.