Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Wenman on May 04, 2017, 10:18:53 AM
-
I know this may be a vaugue question but I am experiencing idle issues. I have a cb550 and have completed a top end rebuild replacing all gaskets, purchased a set of completely overhauled carbs from carburettor Keith in Oregon which were jetted at 100 mains 40 idles, synced and bench tested with a 'bolt on and go' promise! Static timing is adjusted spot on, valve clearances done new plugs etc.
It starts and runs up through the rpms fine however for it to start and run in this manner I need the choke on at 20% all the time?? Idle/air screws turned out 1 revolution!
The engine is running very hot too, after a 10 minute slow ride I cannot touch the rocker cover at all as it will scold my hand and could prob cook my breakfast on it?
The project is almost complete I'm just trying to resolve this problem so I can enjoy the fruits of my labour!!
Please help!!
-
Have you vacuum synced them whilst on the bike? that usually helps to smooth out the idle, bench syncing them gets it close but it needs to be done on the bike really. I would double check all the valve clearences, vacuum sync and see how it is then.
Phil
-
Sounds like you're running lean. Check your inlet rubbers (carb to head) for air leaks...
-
Thanks for your comments so far! Haven't had them vacuum synced in the bike yet so will look into that, a friend has a vacuum sync device so I'll borrow it hopefully it's not too difficult to do myself??
Also has original rubbers between carb and head, nothing obvious apart from what looks like surface cracks, wonder if replacing these would be be worth while anyway?
-
Definitely replace the head to carb rubbers and my advice is use genuine honda parts not repro. Also try to use the original clamps. Get vacuum synced and report back.
-
The only stockist of genuine inlet rubbers hasn't any in stock.. although they do have aftermarket ones? Is there that much difference? Should I hold out for oem?
-
I'd stay well away from syncing the carbs for now. If as James suggested it's got an air leak, then syncing will do nothing but put error onto your carb setup.
If it's leaking air into the engine after the carbs have metered out the fuel, then it will run lean and no amount of syncing will correct it. Air leaking in has no fuel added to it, you have to make sure you've got no leaks first.
If you just want to add fuel to make it run better while you do further diagnosis, then consider lifting the needles one notch to help avoid over heating. Get the engine warm and while ticking over spray something like wd40 onto the intake rubbers, if you get a change in rpm then it proves it's sucking unmetered air in through those carb mounts.
Syncing really is the icing on the cake IF everything else is confirmed as correct first.
-
+1 for the leak test, but also test the seal between the manifold and the head as one of those o-rings might have failed.
-
the inlet o rings are the same as the tappet cover o rings, if they are easier to get hold of?
-
I assume by replacing the head to carb rubbers you mean the boots that actually connect the carbs to the head via the two jubilee type clips per boot. I've already replaced the rubber Oring seal at the inlet manifold!!??
-
In that case spray some starter fluid around all carb to head rubbers and where the manifold bolts to the head to see if theres a leak anywhere. Sometimes the carb rubbers can be overtightened, pinching them and allowing a tiny gap
-
Be careful with flamms / volatile liquids around it in case it goes wrong. Don't do it in a garage and have some means of extinguisher available.
Some people use brake cleaner or carb cleaner to do this and some brands have acetone in them, obvious risks to paint and plastics.
-
So rather than mess around trying to discover any potential air leaks I've decided to order new rubber boots (genuine oem). This will mean carbs to head everything new!!
Professionally rebuilt carbs, balanced and synced on test motor, new boots with original clips, new manifold o'rings at the inlet manifold! This will hopefully mean no leaks! I can then put the balancer on and check there synced correct! Fingers crossed once the boots are changed the problem will be solved! I've added a pic of the carbs if anyone is thinking of ordering from this guy I highly recommend!!
-
lovely pic of the carbs,
I notice you have non-standard filters,do they have internal bell mouths? some times carbs need a bell mouth to smooth the intake air flow,
I hope others here can explain more,and better
-
I hope someone else can explain too as I have no idea what a bell mouth is?
Waiting patiently.....
-
your jetting is going to be way off (lean) if your running stock jetting. 40 pilot, 100 main and stock needle clip position (2nd from top) with those pod filters
I ran 42 pilot, 110 main and needle clip in the middle position (3rd from top or bottom) and it ran pretty damn good, for pods.
a bit of an erratic idle was always a problem I had, pod filters don't really lend themselves to a smooth idle, at least not on 550 carbs. My bro runs UNI foam air filters, oiled and that idles better than my k&ns ever did.
Going back to an airbox was the best choice I ever made, Honda really knew what they were doing.
Hope this helps
Phil
-
Ah, k&n style filters. I tried these, gave up on them as the bike was tempremental as a tempremental thing with them fitted. It worked after a fasion but nowhere near as good as stock setup. I have one bike with a genuine K&n filter that sat under the seat and fitted the standard phlenem chamber so the bike looked stock and with that it was genuinely running very well indeed and had more power than my stock 550k3 which was good going for a cb500 that had been round the clockand some. I do think those filters can work, but you need to be quite skilled and patient to set them up right. I had some on my bmw twin, great on that setup, and my landrover, but the cb I never had the patience to mess around re jetting to get it working right.
-
That is not what I want to hear!! I knew this was going to be a challenging affair hence why I purchased these carbs. The guy came recommended with 35 years of experience in carb building. I told him what set up I had m, pod filters and 4-1 delkevic exhaust and he said he would jet accordingly!
It's strange as it feels so close.. picks up through the revs but won't idle😩
Don't really want to dismantle such beautiful carbs and start re jetting but I think that's where I'm going to end up??
Thanks for all your input I really appreciate it!
-
I have filters like that but run a 110 main jet, runs really well, even ticks over properly.
-
Florence is that with stock idle jets #38? Also what exhaust??
-
i don't know which slow running jets but the exhaust is a 1980s Laser 4-1, very loud.
-
After explaining my problems to the carb supplier this was the response..
I am at a loss from here to determine what your real problem is. I do know that those carbs should not be your problem. No one but the ill advised uses 110 mains on a motor with 4-1 pipes. Are the plugs still black? Have you moved the timing plate around a little to see if that changes anything. There are also idle mixture srews that will need to be adjusted but you can't do that until it will idle on its own.. Have you tried a power balance to see if all cylinders are actually firing?
Like I have said before the carbs were run and setup on a known good motor and they passed all tests on that motor.
I still want to help but I can't drive over to see what you have to work with.
Any other ideas on this guys??
Alan
-
i use 110 main jets in my 550, and that has a stock airbox and 4 into 1 pipes, the hotter cam leans it out a bit though.
Theres no way itll run right with stock carb settings and pod filters, im sure everyone here will agree. Any change to the air supply of the bike will require a change to the fuel supply, more air (pods) = more fuel needed ( bigger jets/higher needle)
-
My carbs came with #38 idles and #98 mains so I'm now running #40 idles and #100 which is what was supplied after informing the carb builder of my set up and what he is clearly standing by!
-
You've got PD46 carbs. On a standard setup the idle screw should be 1.5 turns out +/- 1/3rd turn. Before you start buying things can you say what colour all your plugs are or give us a photo? From my experience the manifold rubbers either have to be in a pretty shocking state to leak or they're not fully pushed home onto the manifold, and for all of them to leak is pretty improbable. Funnily enough I vacuum synched my carbs today and (although I have no leaks) it was pretty amazing how smooth my tickover was with the standard number of turns. I assume you have the needles on the 2nd notch from the top?
-
Ashdowner, the screws are 1 turn out and it is running lean according to the plugs! Also the engine is running very hot which I believe also indicates lean!
I think to Richen the mix you screw the screws in but to make up this leanness would prob have them screwed right in! I believe needles are on the second notch!!
-
The carbs aren't the dreaded PD carbs, good news there! there is a picture of them on the first page, they are either 069a, 022a or 627b(cb500)
You should be okay with the 40 pilots at idle but 100 definitely isn't enough of an increase in the main jet, and without the needle clip moved to the 3rd it just won't cruise right, constant adjustments and increases in the throttle will be needed to maintain speed, ask me how I know.
Your right, in with the screw richens the mixture
-
Phil they are the 627b carbs! Even though it's a pain to change the needle clip I can can do it! I do have 105, 110 and 115 main jets for the 069a's which came off the bike. If I changed the main jet would needle adjustment still be required?
It's not idleing that I'm having issues with and I thought the idle jet would be the one which needed changing not the mains?
-
Sadly I have de tabbed the bike as part of the project so can no longer reserve and put stock air intake back on! I assume you can run these carbs on the 550?!
-
the 500 carbs are fine on the 550, they were just jetted differently from the factory
If you dont have the airbox to put back on, your just going to have to work with what youve got, either way youll definiely need to drop the needle clip to the 3rd slot to richen up the mid range, if youve already got 110 and 115 main jets throw either of them in, 115 if your exhaust is particuarly open and see how it pulls with wide open throttle
I have seen aftermarket pilot jets that are alot shorter than the stock keihin jets, do your pilot jets have a logo on them? oem keihin is always better. That may be causing your idling issue.
These adjustments need to be made to run right with your set up anyway, regardless of the idle being the main concern right now.
what rpm are you idling the bike at?
Also what position is the choke lever in when your running it, it wouldnt be the first time the position of choke on and off was confused (the thump tab on the choke lever becoming horizontal is full choke)
Phil
-
definitely worth trying different jets. have you done a plug chop to note the colour?
even though my bike is non-standard it runs very well and smoothly so it can be done without the standard air box, just requires a bit of patience to set up.
-
Sorry my mistake they aren't the carbs I said. Specsavers here we come. Tip - replace the brass screws that hold the needle slides to the lifting arms with stainless steel capscrews. Getting a screwdriver in is not easy but an allen key is much slimmer and makes it far easier to unscrew them and get them back in again.
-
Turns out having taken the bowls off today that he has put #38 idles jets in and #98 mains jets in!!!
-
Thats stock jetting I'm running 40 pilot and 110 main 1 1/2 out on the a/f screw. That's with 069a carbs, unipods and 4 into 1 header with a short reverse megaphone.
-
Hey gordo,
What position is your needle???
Thanks
Al
-
Honestly can't remember if it's third or fourth down. Think I'm third down but did drop to fourth at one point.
-
2nd from the top is stock, 3rd should be good, 4th will most likely be too rich, unless the engine is hopped up a bit