Rough Cold Start, High Idle When Warmed Up

[ipmaham]

Please correct me if I am wrong...

Just started to ride the bike normally these last few weeks (bought it a month ago), and I have noticed that the cold starts can be a pain when getting the bike to start.

Cold Starts usually goes as followed...
-Kick start twice + little throttle, to get it up and going.
-Will die immediately if I don't give some gas.
-Choke actually seems to make start up worse.
-Once it has been given gas while sitting for 2-5 minutes it will be almost fine. Or driving it right from the get go and making it "work" seems to get things running fine.
-After all is good and the dying stops, it usually idles around 2/2.2k. Seems a little high, don't you think?

Previous owner says he just had the carbs cleaned (we all know it's his word I'm going off of). I was assuming the air to fuel ratio may be a little off, and that's why the throttle seems to balance things out and help it from dying. Correct?


Any suggestions to getting this running better would be greatly appreciated.


Thanks,
ipmaham

 

[retiredgentleman]

It sounds like you have carbs that are not working properly. Yeah, every PO always says the carbs were cleaned...............it means nothing, and they may have made the carbs worse.

A weak battery can make the engine run like crap. Make sure you have a good battery and make sure its fully charged.

In the "Tech" section..................find the "Carb Guide" and read it all.

You have no knowledge of the carbs, so now is the time to take them apart and inspect all parts. You will want to compare the jets you find with the "table" that is in the "Carb Guide".

Hard to start cold likely means the choke circuit is not working. The bottom of the float bowls has a very tiny orifice that feeds fuel to the choke. If you find it plugged, clean it.

 

[crashcourse]

Also, check for air leaks into the intake. If the carb boots are cracked it will let air in and throw off your mixture. Spray a little starting fluid or WD-40 on the rubber parts and listen for the idle to change. If it changes, you're sucking in extra air.

Or the idle may have been set too high by the PO to mask a problem elsewhere, so do everything RG said even if you do fin a leak.

 

[ipmaham]

I was going to verify/experiment with the two mixture screws, sync adjust, and idle adjust too see if this would be a quick fix. If not I will resort to cleaning the carburetors. But I can't find the information for the manufacturer's recommended settings, all I found was a warning from the service manual to not touch them. But that was for when the bike was new, considering I don't know if the PO ever adjusted them I might as well verify their accuracy.

- I've read that the two mixture screws are supposed to be set 3/4 turns out.
- I do not know what the recommended sync adjust should be at.
- I do not know what the recommended idle adjust should be at.

I will be making note of the turns they are currently set at.

Any information or link to the correct manufacturers specification would be greatly appreciated.

 

[5twins]

- the recommended mix screw setting depends on the year of the carb set. Since you didn't provide that, no one can answer your question.

- there is no recommended sync adjust. You set it to where the carbs are in sync, as shown with a gauge of some sort.

- you set the idle speed screw to obtain a 1200 RPM idle (warm).

 

[Jaydela180]

Damn twins, just spent 20 minutes typing a response that was prefaced with" I'm sure one of the gurus will answer your question before I post this, but here it is anyways." You guys a quick.

 

[ipmaham]

- the recommended mix screw setting depends on the year of the carb set. Since you didn't provide that, no one can answer your question.

- there is no recommended sync adjust. You set it to where the carbs are in sync, as shown with a gauge of some sort.

- you set the idle speed screw to obtain a 1200 RPM idle (warm).

-the recommended mix screw setting depends on the year of the carb set. Since you didn't provide that, no one can answer your question.
1977 XS650D (BS 38 Carbs)


- there is no recommended sync adjust. You set it to where the carbs are in sync, as shown with a gauge of some sort.
Ok, so there is no recommended sync adjust... but what do you mean about gauging it? By it's sound, feel, ride?


- you set the idle speed screw to obtain a 1200 RPM idle (warm).
Kind of figured that, just wanted to verify.

 

[5twins]

The recommended mix screw setting for your '77 carbs is 1 1/2 +/- 1/2 turns out. Set them to 1.5 and fine tune from there. If everything is right with your carbs, you should end up somewhere in the range they give and also pretty close to the same on each carb. That 1.5 turns out is just an initial setting. You may not end up there but that's fine. Your bike will tell you what it likes best by the way it runs. As an example, I just set the screws on a '78. The spec for that carb set is 2.25 turns out. After dialing them in, we ended up at about 2 5/8 turns out. That's where the bike ran best.

You use actual gauges of some sort to read the vacuum signal from each carb. Search "carb sync" and you'll find out all about it. There are ways to do it without gauges but they may not give as accurate a result. Search "dead cylinder method" and "bench sync".

 

[ipmaham]

The recommended mix screw setting for your '77 carbs is 1 1/2 +/- 1/2 turns out. Set them to 1.5 and fine tune from there. If everything is right with your carbs, you should end up somewhere in the range they give and also pretty close to the same on each carb. That 1.5 turns out is just an initial setting. You may not end up there but that's fine. Your bike will tell you what it likes best by the way it runs. As an example, I just set the screws on a '78. The spec for that carb set is 2.25 turns out. After dialing them in, we ended up at about 2 5/8 turns out. That's where the bike ran best.

You use actual gauges of some sort to read the vacuum signal from each carb. Search "carb sync" and you'll find out all about it. There are ways to do it without gauges but they may not give as accurate a result. Search "dead cylinder method" and "bench sync".

I was reading somewhere here that before you mess with valve adjustments, you must first verify cam chain tension... And that they must be done in this order.

1. cam chain tensioner
2. valve adjustment
3. timing
4. sync carbs

Will messing with the carbs first possibly throw the rest out of sync?

 

[5twins]

No, it won't effect any of those other settings but if they are off, messing with your carbs can just be a waste of time. All those other things need to be set correctly first, then you do the carbs last. You can try fooling with your carbs, it may help, but if one of those other settings is off enough you may not get anywhere with carb tinkering.

 

[ipmaham]

No, it won't effect any of those other settings but if they are off, messing with your carbs can just be a waste of time. All those other things need to be set correctly first, then you do the carbs last. You can try fooling with your carbs, it may help, but if one of those other settings is off enough you may not get anywhere with carb tinkering.

Understood. Looks like I may have a busy weekend ahead of me. I will report back with results just in case someone else is experiencing the same problems.

Appreciate the advise, everyone.

 

[5twins]

You can and should get the carbs somewhat close 1st so the bike will run. It's going to have to sit there and idle while you check the timing with a timing light. Then, after doing all the other settings, you can revisit the carbs and give them their final, proper tune.

 

[ipmaham]

You can and should get the carbs somewhat close 1st so the bike will run. It's going to have to sit there and idle while you check the timing with a timing light. Then, after doing all the other settings, you can revisit the carbs and give them their final, proper tune.

Will do, thanks.

 

[Dastommy]

Do everything 5twins says. He helped me out with mine and she purrs like a kitten

 

[ipmaham]

Bike sounds best with the mixture screws turned 2 whole turns out. Starts with one kick. Idle is about fine.

Problem...
Upon start up, bike idles around 2k rpm. A twist of the grip and it shoots up to 3.5k rpm's, stays, and then slowly (3-7 seconds) come down. It will eventually die though after a few minutes.

Found this weird too... Bike standing straight up does the above while idling. Lean it to the right and rpm's shoot up to 3k rpm while idiling. Lean it to the left, rpm's drop and the bike dies. I found this very peculiar.

Also, bike will sometimes just idle high for no reason what so ever.

Going back to tweaking it. Any feedback would be appreciated.

 

[nj1639]

Throttle cable routing?

 

[ipmaham]

I checked it and made sure there was too much/less slack. Also made sure it wasnt getting stuck.
Wouldn't know what else too look for.

 

[5twins]

If you haven't done so, I would check the float levels. The bike seems to be exhibiting lean conditions. The racing idle, slow to return to idle, the required 2 turns out on the mix screws, all point to being too lean. The fuel levels in the bowls may be too low. There's also the possibility that you have an air leak somewhere. I would also check the advance unit to make sure it's operating smoothly and not hanging open.

 

[ipmaham]

Float level for a xs650d should be 25 +/- 1mm, correct? I'll have to take it out and check, never done it before.

As far as checking for air leaks, spraying carb cleaner around the carburetor and listening for idle to die a bit works from what I heard. Not sure what else does, I'll have to look in to it. It will just be difficult since it likes to vary on its own sometimes.

The advanced unit, should a properly working one snap back to it's opening positions after pushing the the levers inward? And not get stuck like the video here? If so, that'll be the first thing I do today after work. Seems simple enough.

 

[weekendrider]

You can use canned carb cleaner but it isn't nice to rubber bits.
If you have a hand held propane torch it would be better.
You will be listening for an increase in the rpm's as the motor picks up the fuel from the leaking area.

You might as well dive into them carbs. If you ride one of these you WILL have to become familiar. Sooner or later.