Topic: 1973 Honda CB500 Four with idle issues.

[kaptainkid1]

I have found a 1973 CB500 Four sitting for couple year and decided to clean it up and get her running. I am looking for advice on carb tuning or idle issues. My setup is as follows:
 - MAC 4 - 1 Exhaust
 - Stock Airbox
 - Stock Cam
 - Stock Carbs
 - Stock Airfilter
 - Stock jets and needle new from ebay for my model.Rebuild kit.
 - I'm located at sea level.

The carbs were pulled off and each one was sonic cleaned in 50/50 pine sol.

I have valve adjustments set, timing is correct, carb synced with vacuum gauge , new plugs and new oil.
The bike runs fine and power band is good to excellent when opening throttle. No hesitation or flat spots. It seems the bike is running fine when the bike is moving. The bike starts up no problem and idle fine until it warms up. Then on ride it will die if I don't keep revving the engine. Also it seems to get stuck at 2000-3000 rpm at the light or drops below 1000rpms and dies. More often it dies when I come to stop.
I've adjusted the idle mixture screw 3/4, 1, 1 1/2 and 2 turns out. None of these Idle mixture setting works.
I'm not sure but when syncing my carbs, I originally had the idle mixture set at 2 turn out and all four. Does it matter if I set the mixture before or after the carb syncing?
Looking for advice for this strange final problem.

[calj737]

First and foremost, restore your stock needle with the clip in the stock position. Then insure the entire internals are absolutely clean and spotless (especially the emulsion tubes).

If you bench synced the carbs before install, did you also measure the fuel height? Some of your low speed issues when warm could be traced to vacuum leaks. Inspect the boots, around the manifold at the head, and see if spraying an aerosol effects the idle speed. If so, you have a leak.

[Bankerdanny]

Don't assume that the brass from your rebuild kit is actually the stock sizes no matter how it was advertised. The original brass really doesn't wear out. Clean it (a high 'e' guitar string will help you with clogged jet holes) and reinstall all of the original brass then set needle height and air screws to factory specs. All the eBay kits are really good for (unless you luck into NOS Honda parts) are the gaskets and o-rings.

[kaptainkid1]

I just sprayed carb cleaner for air leaks around the rubber boots and carb sync screws. It didn't have any leaks and the bike idle fine. I didn't run the bike for long but I'm sure once its starts to warm up it will cut out.

Does anyone know the correct air fuel mixture idle screw should be set at? I have it at 3/4 turn out now.

As for the brass was good but all the rubber rings were dried out so I had to put the new ones.
I did keep the olds but it didn't run right with them cleaned and put so I had to buy a rebuild kit.

 

[Scott S]

 You can get O rings for the old brass. I have pictures on my PC of why you shouldn't use reproduction brass.....I'll post later.

[Bankerdanny]

I just sprayed carb cleaner for air leaks around the rubber boots and carb sync screws. It didn't have any leaks and the bike idle fine. I didn't run the bike for long but I'm sure once its starts to warm up it will cut out.

Does anyone know the correct air fuel mixture idle screw should be set at? I have it at 3/4 turn out now.

As for the brass was good but all the rubber rings were dried out so I had to put the new ones.
I did keep the olds but it didn't run right with them cleaned and put so I had to buy a rebuild kit.
 

You don't have to replace the whole jet because the rubber o-ring is perished. Just remove the o-ring and replace it with one from the kit. You need to really make sure the jets are spotless. I spray carb cleaner through each jet to make sure I get a nice mist from each of the holes. You also need to make sure that the holes on the side of the emulsion tubes are clear.

The factory air screw setting is 1 turn out +/- 1/8th

[kaptainkid1]

Here is link to rebuild kit from ebay.

http://www.ebay.com/itm/360795207303?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

These seem to be ok and I know people have warned me about using them. Let me know if these might be the problem.

Honestly, I'm not 100% sure if the old brass was original either, since the bike had a couple owners and the last owner was going to change it to a caferacer and I saved it and changed it back. It seems it needed a little tlc and now it's at this stage.

So the old brass is questionable...maybe and new brass can be ok too right?

I've changed the brass on my cb750 with ebay stuff and those carbs sync and it run fine.

[Bankerdanny]

You should be able to determine if it is original based on the markings. Original Keihin parts should have a K on them.

[Scott S]

 I feel like I've posted this picture a thousand times now, but if it helps anyone to not go through what I went through, it's worth it.
 I chased a hanging idle issue for months. I tried every conceivable thing. This particular bike was my first SOHC4 so I didn't know at the time that the jets were not stock. I installed the correct, genuine Keihin pilot jet (far left in the pic) and the issue was fixed IMMEDIATELY.
 I strongly recommend checking the "kit" you used and sourcing Keihin parts if needed. The Keyster kits also have the wrong profile on the needle. Only use genuine Keihin/Honda brass bits. It makes a difference...a BIG difference.

 And, of all the bikes I've owned, the SOHC4 is most sensitive to fuel level in the bowls and, especially, carb sync.

 

[kaptainkid1]

ok I think I have the left jet and I'll put back the old one because I'm having the hanging issue too.

[flybox1]

Dont put those carbs back on your bike till the needle clip is in the stock slot, and you've clear tube tested all bowls, and adjusted (if needed) all floats to have 3mm below the top of the carb bowl fuel level.

[Scott S]

 And if you used the needles from the kit, put the stock needles back in.

[kaptainkid1]

OK I just cleaned the Keihin jets and she back in the carb. The floats and needles were never a issue. She seems to run much better now. No more dying at stops. Going to rider for 1/2 hours get her hot and see if I still have same problem..

I used the Keihin Jets to the right. I had them cleaned on polished. The ebay jet #40 are to the Left and out.

[Scott S]

 You used the ones on the right in your pic....next to the box, right?

[kaptainkid1]

Yes I used the old Keihin brass Jets to the right....

So the problem didn't really go away that much. As I suspected the bike needs to be hot and the dying and idling between 2000-3000 rpm came back. After revving the engine hard it might come down to 1000 rpm once and awhile.
I think cleaning the carb body might have been the problem or my fuel line hitting the intake manifold might be creating vapor lock or heating the fuel prematurely.

1st:
So the process of cleaning my carb body might be the problem. I took the only the body and the jets, bowls, hardware from the bottom end apart but left the slider and needle in the carb body alone during the dip in 50/50 pine sol sonic cleaner over night. Before I take those carb set apart again, here are the old and new needles from one of my back up carbs. The needle was set at 1 notch from the bottom. shown in the picture.
Left Old Needle and Right New ebay Needle. 
Should I just clean and leave the old needle back in?

Since all the carbs needles and slider are attached to returning spring I feel this isn't the issue. The needles are not bent or dirty. They return back to the closed position every time. I don't have any hang ups when carbs go back to idle, but I never took this section apart to clean them. So should I dismantle each carb body and clean the needles and sliders?

2nd:
Next possible problem is fuel line heating up.
Since I had rust flakes clogging the carbs from the old gas tank. I coated inner tank with a tank sealer and it's all good.
I also attached fuel filter to both lines but I it might be unnecessary. Take a look at the photo because I noticed the fuel line was right next to engine block and intake manifold. Very hot area.




Also what are these parts from the rebuild kit?
Do I need to replace these pieces too?



At the bottom of the carb body the carb needle drops into a brass nipple but these pieces don't come or can be replace correct?



I do recall on my cb750 carbs they come out and can be replace but not the cb500 carbs right???



What do you guys think I should do now?

[jonda500]

That 'brass nipple' the needles drop into is the emulsion tube (in the manual it's called the needle jet). They are removed from the bottom (in the float chamber) after removing the main jet. These need to be clean - they may need to be pushed out from above.
John

[Scott S]

 Use a wooden chopstick or something and tap them out from above. They will come out of the bottom of the carb.

[Deltarider]

As far as removing the needle jets (aka emulsion tubes) I always had success doing it like this.  After removing the main jets twist the throttle wide open so the slides and the needles will raise. With your free hand insert from below a match or wooden toothpick into the needle jets. When that is snug in the needle jet, cant or turn the wooden toothpick a mm or so and you can wiggle the emulsion tube out easily. Some WD-40 at forehand can help. Essential in this procedure is that you open the throttle so the needles will be up. BTW, sometimes the needle jets just drop by themselves after the main jets is removed so start with your hand cupped under it. This way you won't have business at the top of the carb and so saves you a synchronisation.

[strynboen]

looks like the fuel line are bend to hard at the extern filter..does it flow real good..?

[Deltarider]

Well spotted Strynboen, unless it's a kind of elbow. For me extra fuel filters have been causing nothing but trouble. When the petcockfilter is still there, no need for an extra filter. On the 4-4 500/550s that originally had these oldstyle carbs, fuel lines standard length were 18 and 30 cm with the oldstyle petcock and 17 and 28 cm with the new type petcock. Ideal diameter is Ø 5,5 mm. Guaranteed no kinking!

[Moosey]

With the 4 into one exhaust, should he get different jets?

[Deltarider]

Hard to say. I remember 4-1 aftermarket brands used to advertise with: no rejetting required.

[Scott S]

With the 4 into one exhaust, should he get different jets?

 Depends on the brand of the exhaust.

 MAC generally uses stock jets. Others may (or may not) require minor bumps to the main.

 Start adding pods, no muffler, etc., and all bets are out the window. It's best to list exactly what you have and what you're trying to do.

[kaptainkid1]

Oh Jesus, the problem is still going on and I used some seafoam in gas and road it for 100 miles.
I was hoping it would clean the carbs sliders, emulsion tubes and needles if they weren't clean enough from the pine sol 50/50 mix. Which the whole body sat over night.
Since everything is stock from airbox to carb needles, jets. I'm stumped if the 4 into1 MAC exhaust is hanging up the rpms when the bike is hot. Since you guys mentioned it. I'm guessing no..everything i've read about MAC exhaust is stock jets are fine.

I'll pull the carbs off one more time and clean it very well from sliders, emulsion tubes, sonic clean each carb body by them selves. Plus making sure to replace old Keihin brass back into the carb body.

will report back if this works.

[calj737]

Much earlier in your thread it was suggested that yu measure the fuel height in the bowls with the clear tube method. Have you done so? If, pictures would be helpful.

Also, with fresh plugs, perform an idle chop. Once these 2 baselines are established, tuning should commence. But chasing what you believe to be issues without verifying these critical conditions will lead to further frustration.