Good valves, but hard starts? Now with clean chokes and a new top end!

[MisterCinders]

This is a gritty reboot of my prior thread. A lot has happened since then, so I fired up this new thread.

First, an update on the bike and maintenance.

• I have a fresh 850 top end on the bike.
• Valves are adjusted to nice clearances.
• New exhaust gaskets installed during the rebuild.
• New intake boots and o-rings as of earlier this summer.
• Carbs freshly cleaned (strip, dip, full monty) during the 850 rebuild.
• Based on feed back in the earlier thread, I paid close attention to the choke tubes and passages. They are clear.
• Floats are at 24mm, and the carbs do not leak or flood.
• K&N Pod filters (don't hate) freshly cleaned and lightly oiled.
• Ignition timing checks out.
• Spark is good on all four cylinders.
• Carbs bench synched and then vacuum synched. I get a little vibration and rattle still, so I may revisit the vacuum synch once more tonight.
• Fuel screws are 1 turn out
• Air screws are 1.75 - 2 turns out.
• Pilot jet 15
• Needle is at 4th slot
• Main jet is 117.5

So with that baseline, here are two small issues.

Hard Starting

Starting the bike cold is still strange. It's like there is a hangover rev from the night before. Even without choke, the first hit of the start button will fire and the engine runs for about a second. It sounds like revving and chopping.

Then it acts like a cold bike. It will start with a lot of choke but sometimes needs the idle screw dialed in to get with the program. It tends to be choke needy until I can get one good rev in. So with it idling on choke, I can kill the choke and blip the throttle to "catch" the revs. But I have to make the choke to rev transition quickly, similar to finding the friction point with a clutch/throttle. Otherwise, throttle with choke on tends to bog the engine. If I can do that kill choke/blip throttle quickly enough, the bike immediately idles nicely, will pull out in first gear fine, etc.

If I had to dial in the idle screw to start it, after a few minutes of riding the idle settles in too high (e.g. 2,000 - 2,500). When I ease the idle screw out a bit, it will idle at about 1,100 nicely. No real surprise that the idle climbs early on, since I usually have to increase the idle screw to start it.

After riding for 10 minutes or so. The bike will start right away with no incident. Only if the bike sits for a few hours or overnight, do I have this issue.

I know what you're thinking - it's lean! You need choke and the idle climbs when warm. But, not so fast. There are several factors weighing against against a simple lean issue.

• The plugs are a lovely tan color.
• The idle doesn't hang on blips and the engine pulls fine.
• The only climbing element is that as the bike initially warms up, it settles into the higher idle setting needed to start the bike up.
• It doesn't feel flat or miss or do anything else to misbehave at low speeds/throttle.

Yes the pods and pipe increase the airflow, but the plugs indicate that my jetting adjustments are covering that. There are no air-leaks with new boots and rings, etc.

What's most odd to me is the "leftover rev" on that first starter hit. And the immediate transition from problem child to easy riding once I get one good rev on the engine. BTW - idling on choke for ages doesn't seem to make a difference. I still need that one good rev whether it warms up for several minutes on choke or just a few seconds. If I close the choke without a blip, the idle dies.

I considered the possibility of a petcock/vacuum issue, but this happens on PRI as well as ON. My petcock is new and shows no leaks or other problems.

Midway Exhaust Pops/Gurgles

This may just be a mixture issue, despite my healthy tan plugs. I have a good amount of popping in the exhaust, but not at the header nor the tail end. In other words, there is a gurgling/popping noise during the idle from the middle of the pipe. No flashing out the muffler or popping noises near the head.

Popping there seems like a richness issue (unspent fuel goes to pipe, heats up, BANG), but I have no bogging and my plugs show a nice tan.

Any ideas?

[Steve]

I just went back and looked at your previous thread, and it appears that everything has been done somewhat correctly.

You say your plugs are tan, which is good, but what was happening to get them to that color? Did you come off the street (probably on the needle circuit), then idle into the driveway (probably not long enough to re-color the plugs)? I am not saying you didn't do proper plug chops, just haven't seen you say what you did.

I agree with the others that your enrichening system appears to be plugged. Blowing air or carb spray through the tubes won't always clear all the gunk. I use a single strand of copper from a piece of electrical wire to poke through the entire length of the tube. Then, make sure the well in the bowl in which the enrichener tube sits is open to the fuel supply in the bowl. I have seen that passage plugged, too, which is why I always dip the bowls when I clean the carbs.

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[hampshirehog]

Then, make sure the well in the bowl in which the enrichener tube sits is open to the fuel supply in the bowl. I have seen that passage plugged, too, which is why I always dip the bowls when I clean the carbs.

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This is very common and very often missed. The enrichener circuit won't work at all if they are clogged. You need to spray something though that hole to check it's clear - don't just rely on a visual.

[Steve]

This is very common and very often missed. The enrichener circuit won't work at all if they are clogged. You need to spray something though that hole to check it's clear - don't just rely on a visual.

Yep, I dip them with the other carb parts to sften any crud, then spray the opening (WEAR SAFETY GLASSES FOR THIS ), followed by a wire poke, if necessary, and finish it off with a blast of air.

.

[MisterCinders]

I just went back and looked at your previous thread, and it appears that everything has been done somewhat correctly.

You say your plugs are tan, which is good, but what was happening to get them to that color? Did you come off the street (probably on the needle circuit), then idle into the driveway (probably not long enough to re-color the plugs)? I am not saying you didn't do proper plug chops, just haven't seen you say what you did.

I agree with the others that your enrichening system appears to be plugged. Blowing air or carb spray through the tubes won't always clear all the gunk. I use a single strand of copper from a piece of electrical wire to poke through the entire length of the tube. Then, make sure the well in the bowl in which the enrichener tube sits is open to the fuel supply in the bowl. I have seen that passage plugged, too, which is why I always dip the bowls when I clean the carbs.

.

Um "somewhat correctly"? You flatter me, Steve.

At the end of my rides (which include a good amount of city riding at the return end), I chop the throttle, hit the kill switch and coast up the alley to my garage. So it's a decent idle circuit plug chop. It would be better if there weren't huge speed bumps in the alley. I have to clear those before cutting the throttle, but it leaves me a good 50 ft to coast.

I will pull the bowls and check those tubes again.

[MisterCinders]

Any ideas on the weird exhaust pops? Header popping on decel would be lean. Muffler backfires are usually rich. What would mid pipe noises indicate?

[capnjim]

My bike was doing something similar. (1978 GS750)
Sounded like it was rich, with lean looking plugs. I now have my pilot air screws out less than 1/2 turn. Might not make sense, but it runs pretty nice. I started at 1.5 and it was always kind of lean. I kept sneaking them in a bit, now, at half a turn, the bike runs great.

[MisterCinders]

I cleaned the bowls and the choke tubes. A wire clears all the passages.

Still have the weird starting deal.

One possible clue on the choke. I cleaned up the rail some time back (it was pretty caked in grime), and ever since then it moves very freely. I think it may be creeping closed on me, as I can pull it open fully, but then tugging it will up the revs.

Re-synched the slides. The Carbtune showed them to a little off, and the fresh synch has smoothed out the rattle a bit. So there's that.

Will continue to fiddle with the pilot screws to work on that popping. Before the 850 swap, the bike always ran a bit rich - even with pods and pipe. Now with fuel screws at 7/8, it showed lean plugs and at 1 turn out, the plugs look good, but the popping could be a lean pilot still. Might swap the pilots out for 17.5s.

[MisterCinders]

Ran another chop and the plugs looked a bit lean, which was a relief as it matched the symptoms.

Changed the pilots to 17.5 and did another chop. Even more lean.

Also pulled my intake boots and orings (both are new this summer) to make sure they were not loose or cracked. Soaked the rings in fuel while I worked the carbs to plump them up, but all looked good.

Set fuel screws to about 1 1/4 turns. Then tried a hardcore highest idle. Turned air screws in until it began to struggle, then backed them out until normal idle resumed.

That put the air screws pretty far in, maybe a turn out.

Checked this with the Colortune, got nice blue inside. Backed the air screw out a touch more but kept the flame blue.

Was too late for a good ride to test, but a short ride and chop showed better coloring on the plugs. The popping is almost completely gone.