1979 CV carbs will not idle

Leslie

Leslie

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Lads the bike has the standard carbs Mikuni CV she starts up on full choke after several turns of the engine on the start button, when i switch the choke off after a few minutes she dies and will not tick over, any suggestions, the previous owner had the carb ultrasonically cleaned, i'm thinking pilot jet.

I do not have any schematic/diagram/illustration of the carbs
 

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Leslie said:
Lads the bike has the standard carbs Mikuni CV she starts up on full choke after several turns of the engine on the start button, when i switch the choke off after a few minutes she dies and will not tick over, any suggestions, the previous owner had the carb ultrasonically cleaned, i'm thinking pilot jet.

I do not have any schematic/diagram/illustration of the carbs
Click to expand...
I‘d check the pilot jets. You can drop the float bowl with carbs still mounted and pilots are in the bowl. If they are clean, then the circuit may be plugged up and unfortunately requires carb removal. I just went through this myself.
 
AndersJ said:
+1 pilot jet. Maybe it’s overkill but I always pull the carbs on a new to me bike. Then you KNOW what brass is in there and that they are clean and float heights and needle positions are correct.
Click to expand...
The carbs have been cleaned and re-built apparently,,,,, looks like a strip and rebuild then, is the std pilot jet for the carb is +1 pilot.
 
Leslie said:
The carbs have been cleaned and re-built apparently,,,,, looks like a strip and rebuild then, is the std pilot jet for the carb is +1 pilot. drop the bowls first
Click to expand...

Yeah the “apparently” is what will leave you chasing your tail. Just get in there and see what’s is actually the case. By +1 I meant I agree, check the pilot. No comment on what the appropriate size should be.
 
Will the bike idle once fully warmed up? If so then your idle speed may simply be set too low. These bikes will idle very low, maybe even stall, when cold. Idle speed will increase as the bike warms up. The trick is to get the speed adjusted just right so it will idle cold without stalling but not too fast once warmed up. Idle speed spec is 1200 RPMs and you should set that when the engine is hot.

You appear to have the typical "pipes and pods" mod. On the '78-'79 carb set, that should require one up on the pilots (#27.5 stock to #30), 2 up on the mains (#135 stock to #140), and the needles leaned a step. However, those tapered K&N style (pleated) pods may mess with main jet size selection, not allowing 2 sizes up without break-up in the upper midrange. Now normally, this would be a sign that your mains are too big, but in your case, it would be the pods causing it. Straight foam pods work best. With them, you will be able to go up the 2 sizes without getting the break-up.

It also appears that you have the type D cam chain tensioner assembly. Put upgrading that to a type E assembly on your "to do" list. For the "how and why", see post #22 here .....

https://www.xs650.com/threads/cam-chain-tensioners.1056/page-2
 
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A couple more things - I see you have no hoses on the engine breather. If any oil comes out, which sometimes it does, it's going to make a mess all over the tops of your carbs. I also see you still have the original rubber washers on the top acorn nuts on top of the motor. They allow those acorn nuts to come loose all the time and head gasket leaks are often the result. Most of us change them out to copper or brass .....

LeftCarb.jpg
 
5twins said:
A couple more things - I see you have no hoses on the engine breather. If any oil comes out, which sometimes it does, it's going to make a mess all over the tops of your carbs. I also see you still have the original rubber washers on the top acorn nuts on top of the motor. They allow those acorn nuts to come loose all the time and head gasket leaks are often the result. Most of us change them out to copper or brass .....

View attachment 209267
Click to expand...
5twins said:
No, in fact you should do that on a head that's never been touched. The nuts and bolts can become stuck on their threads and give a false torque reading - they may read tight when they're really not. I pull the fasteners right off one at a time, clean and apply anti-seize, then torque back up to spec.
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Concerning the headbolt washers, can I remove 1 bolt nut at a time to replace rubber faced washers with copper washers? The quote from 5Twins is from Tech Section "Bad headbolt torquing"
 
Yes, do one at a time while all the others remain tight. I bring each one up to about 25 ft/lbs then once all 4 are done, I go back and bring them up to a final torque of about 28 ft/lbs. I'll go as high as 30 ft/lbs if I'm trying to fix a leaking head gasket but that's my max now. In the past I had gone higher (32 to 35) but it didn't cure the leak and only seemed to put a strain on the studs, so I limit my max to 30 now.
 
5twins said:
A couple more things - I see you have no hoses on the engine breather. If any oil comes out, which sometimes it does, it's going to make a mess all over the tops of your carbs. I also see you still have the original rubber washers on the top acorn nuts on top of the motor. They allow those acorn nuts to come loose all the time and head gasket leaks are often the result. Most of us change them out to copper or brass .....

View attachment 209267
Click to expand...
5T, can you use any thick copper washer or are they a special dimension for this application? I already have the brass washers but am thinking I could have used 2mm thick copper washers I had.
 
5twins said:
Yes, do one at a time while all the others remain tight. I bring each one up to about 25 ft/lbs then once all 4 are done, I go back and bring them up to a final torque of about 28 ft/lbs. I'll go as high as 30 ft/lbs if I'm trying to fix a leaking head gasket but that's my max now. In the past I had gone higher (32 to 35) but it didn't cure the leak and only seemed to put a strain on the studs, so I limit my max to 30 now.
Click to expand...
All 4 or all 8?
 
bosco659 said:
5T, can you use any thick copper washer or are they a special dimension for this application? I already have the brass washers but am thinking I could have used 2mm thick copper washers I had.
Click to expand...
Yes. I'm using 2mm thick copper ones I found at my local hardware store for less than a buck apiece. They do just fine.
 
On a new-to-me bike, I do all 8. The inner 4 don't need copper washers. Those studs don't flow oil so the original steel washers are fine there. I'll also re-do (remove, clean, anti-seize) the 8mm bolt under each spark plug. It is part of the head gasket fastener pattern.
 
I see I missed a question a few posts up about the choke. Yes, the choke, or more correctly called the enrichener, is a separate, stand-alone circuit. Here's a diagram illustrating how it works .....

Starter-Choke.jpg


When you lift the plunger, fuel is drawn up from the float bowl through a small jet. Air is mixed with it along the way and it's fed into the main bore. Due to it's location at the bottom of the bowl off to the side, the starter jet is easily and often plugged if there's any crap or dirt floating around in the bowl .....

Choke Jet.jpg


If the starter jet gets plugged, the choke won't function and the bike will be very hard to start cold. Here's how to check if it's clear .....

ChokeJet2.jpg
 
5twins said:
Yes, any thick copper washer is fine. Years ago for my '78, I bought Suzuki washers from a dealer. This was the recommended replacement before Mike's started selling the brass ones. Suzuki calls it a "gasket" even though it's just a thick copper washer .....

https://www.partzilla.com/product/suzuki/09168-10017

QPc2pEu.jpg


I still prefer to use copper ones only now from a big bagful I got off eBay .....

https://www.ebay.com/itm/153431432762?ssPageName=STRK:MEBIDX:IT&var=453372990672&_trksid=p2060353.m1438.l2649
Click to expand...

5twins said:
On a new-to-me bike, I do all 8. The inner 4 don't need copper washers. Those studs don't flow oil so the original steel washers are fine there. I'll also re-do (remove, clean, anti-seize) the 8mm bolt under each spark plug. It is part of the head gasket fastener pattern.
Click to expand...
I am going to have 16 extra. Anyone who needs 4 or 8 can have them. Give me an address and zI will even pay postage. I don't want to be a warehouse.
 
5twins said:
I see I missed a question a few posts up about the choke. Yes, the choke, or more correctly called the enrichener, is a separate, stand-alone circuit. Here's a diagram illustrating how it works .....

View attachment 209341

When you lift the plunger, fuel is drawn up from the float bowl through a small jet. Air is mixed with it along the way and it's fed into the main bore. Due to it's location at the bottom of the bowl off to the side, the starter jet is easily and often plugged if there's any crap or dirt floating around in the bowl .....

View attachment 209346

If the starter jet gets plugged, the choke won't function and the bike will be very hard to start cold. Here's how to check if it's clear .....

View attachment 209348
Click to expand...
Does that suggest that there are lots of problems with Leslie's carbs?
 

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