Cold Start - Too Rich? -- RESOLVED --

All,

First I'd like to say thanks. I adjusted the valves, changed the fork seals, and cleaned/synced the carbs. Couldn't have done it without this forum.

So, my 82 XJ650 is running great, except for 'cold' starting. I use 'cold' loosely because it was over 60 degrees today, but I had the same problem. After cranking the engine over for a few seconds, even with the enrichment circuit off, the plugs come out drenched. A quick squirt of starter spray in the airbox though, and she fires right up and runs strong. The bike starts up quick and easy after its warm.

Too rich for cold starting doesn't make any sense to me, unless there isn't enough air getting into the cylinder. Could this possibly be a symptom of some improper tuning (i.e. idle mixture too rich?) or is it indicative of another problem I haven' t thought of?

Thanks,
Cal

 

Re: Cold Start - Too Rich?

I think I may have figured out why the mixture is too rich. The bike won't start or run when the choke is on even a slight amount.

I remember reading the enrichment circuit has its own air jet. If that guy was plugged, turning on the choke would cause the mixture to be too rich and the engine to stall. Has anyone had an issue similar to this?

Thanks,
C$

 

Re: Cold Start - Too Rich?

Is your battery in good condition & fully charged?

 

Re: Cold Start - Too Rich?

Wizard,

Yes, the battery is brand new. I trickled it overnight before I put it on the bike.

Before I cleaned the carbs this winter, the starting procedure was: full choke, bike starts right away around 3500 RPM, turn off choke when warm.

Like I said in my previous post, any choke now will cause the engine to stall out, even cold.

Thanks,
C$

 

Re: Cold Start - Too Rich?

Turn your pilot mixture screws in, a few degrees at a time.

 

Re: Cold Start - Too Rich?

Wizard,

I will give that a try. But I set the mixture with the colortune and then further tweaked it until each plug had a nice tan color. the bike is running so well now (aside from the cold starting/choke issue) that I hate to change it...

Thanks,
C$

 

Re: Cold Start - Too Rich?

I saw mention of a bleed hole in the enrichment tube. I believe I've marked it in the picture below. If it was clogged I think it would produce symptoms like what I'm seeing (choke kills the engine, won't start with choke on & wets the plugs).

I've also tried to mark the air path for the fuel enrichment circuit. I believe if the air path was clogged, It would produce the same symptoms. But those are some pretty big holes to clog...

I also plan to recheck the float heights.

Can anyone think of any other faults that might produce the symptoms I'm seeing? I'd like to knock them all out when I get around to taking the carbs off again.

Thanks!
C$

 

Re: Cold Start - Too Rich?

Your first post said you had cleaned & synced the carbs. :?

 

Re: Cold Start - Too Rich?

If your Main FUEL Jet has got that much build-up in it ... the Emulsion Tubes AIR Inlets are probably clogged shut.
That will make you run RICH because the Main FUEL Jet Supply won't be properly atomized and broken-up by the Main AIR Supply.

 

Re: Cold Start - Too Rich?

Guys,

Thanks for replying.

Wizard, I should have clarified. These pictures are from a spare set of carbs, and yeah, they are disguisting. I've just started taking them apart and haven't had a chance to clean them.

Rick, I will double check the emulsion tubes when I take the carbs off, thanks!

C$

 

Re: Cold Start - Too Rich?

I am experiencing this same issue. In the morning, i can crank and crank, won't fire. Come back at the end of the day and it starts up almost right away. It is not all that cold here, this morning around 10 deg C.

This morning I pulled the plugs, heated them up and it started up , but only on three cylinders. If you ride the bike, what happens to the fuel being pumped into the unfiring carb? Plug is cold and dry.

 

Re: Cold Start - Too Rich?

My bike has same issue, I think Gamuru explains the fix in this excellent post
http://www.xjbikes.com/Forums/viewtopic/t=8918.html

 

Re: Cold Start - Too Rich?

All,

I don't feel like I did a very thorough job explaining the situation. So, with your indulgence, I'd like a clean slate and another crack at detailing the problem.

For as long as I've owned my 82 xj650 maxim, its always started right up, regardless of the temperature. The procedure is:

1. Turn the choke to full on
2. hit the starter, engine fires after only a second or two
3. revs around 3k with the choke on, turn the choke down slowly as the engine warms.
4. warm engine idles around 1200 rpm

This winter I decided to take apart the carbs and give them a good cleaning (many thanks to Rick, Len, and Gamaru for their tutorials). Here's what I did, in no particular order:

broke the rack
drilled out the pilot plugs
replaced pilot o-rings
dipped the bodies in carb cleaner over night
replaced the throttle shaft seals
replaced the float needles with aftermarkets
adjusted the float heights
cleaned the enrichment circuit following Gamaru's guide (spray shot out several feet)
replaced two of the piston diaphragms
clunk tested
checked valves replaced 4 shims
replaced the plugs, gapped to 0.030 inches

The carbs have been synced and the pilot adjusted using a colortune + plug reading. THE BIKE FLIES LIKE A ROCKET. I mean, its running better than I ever imagined EXCEPT for cold starts...

It seems the common cause of problematic cold starts is a clog in the enrichment circuit. My working hypothesis is that instead of not getting enough gas, I've boogered something up and am getting too rich of a mixture with the choke on (even slightly). Here's why I think the mixture is too rich:

1. crank the bike for a few seconds with the choke on, won't fire, plugs come out drenched in gas
2. Start the bike using instant start
3. Turn the choke lever to full on
4. Instead of revving up to 3k as it used to, the engine hovers around 1k
5. a little black smoke, and a definite rich aroma come from the exhaust pipes
6. Leave the choke on for more than a few seconds and the plugs come out fouled pure black.
7. Put in the colortune and the color changes from bunsen blue to orange/yellow when the choke lever is set.

I'm having trouble figuring out what would cause the enrichment mixture to be too rich (too much gas OR not enough air). Here are my theories, please let me know if you have any others or if any of these are completely implausible.

1. Float heights are incorrect. too much gas in the bowls. (I have checked and doubled checked, if anything I have the float heights on the low side right now).
2. Clog in the small hole in the brass tube sticking into float bowl. (See the pictures above, I've checked with a bright light and all of the holes are at least partially open)
3. Accidentally enlarged a jet in the enrichment circuit. (When I was cleaning I used toothpicks to probe the jets. Could that have significantly enlarged them?)
4. Clogged air jet for the enrichment circuit. (I think I've marked the air jets in the pictures above, but please correct me if I'm wrong. They look like they'd be awfully hard to plug.)
5. The overnight carb dip ate away some important rubber gasket in the enrichment circuit, but if there was rubber there, I sure never saw it.
6. Spark is too weak. Coincidence this coincided with my carb cleaning.
6. I've angered the XJ Gods. My punishment is to have a supremely well running bike that I can never start...

Thanks for reading, I know it was a long post but I wanted to get it all out there. I'd even offer a free steak dinner to anyone that can help me get to the bottom of this mystery.

Thanks,
C$

 

Re: Cold Start - Too Rich?

Well, this is a long shot, but...

How did you clean out the jet in the siphon tube of the carb bowls? Did you stick any wire through it? If so, you could have possibly enlarged the opening, allowing too much fuel to go through. You mentioned that you have another set of carbs - you could try swapping the bowls (assuming you can clean out the siphon tubes on the old set WITHOUT running any wires through the jets and risking enlarging them too.) Just an idea...

 

Re: Cold Start - Too Rich?

The Enrichment Circuit is NOT an ON~OFF Choke.

It's a VALVE.
Sounds like you got things Cleaned-up well-enough to not need the whole shot starting the Bike.

Soaking the Body's overnight might have damaged the Shaft Seals, too.
That would cause an Air Leak

 

Re: Cold Start - Too Rich? -- RESOLVED

Well, I found the problem! I believe I forgot to mention it, but I replaced the bowl gaskets as well. I used the cheaper paper gaskets that Chacal sells. I forgot to punch part of the gasket (see below) which plugged one of the air jets and led to the enrichment circuit being WAY too rich. Thanks for your help and considerations!

C$

 

Thats a good one for the books.


MN

 

"Well it just goes to show ya, it's always something"

- Rosanne Rosannadanna

 

Guys,

Bringing this one back to life so to speak - I notice cmoney hadn't punched through the gasket to accommodate the passage which effectively blocked it.

I assume those carbs are Hitachi's as the Mik's have that passage a bit closer to the long brass pick up tube. I had seen before my bowl gaskets also didn't have the holes punched through so I felt compelled this morning to double check and I removed the rack (expert now!) and punched them through.

Back together and she didn't want to start on "choke" but after releasing the "choke" she fired up OK but didn't want to idle well. I suspect I will have to re-synch and colourtune (no big deal) but was just wondering how many of us are running with these passages "blocked" and what the actual implications are.

Frankly, I'm not certain what exactly that passage does but it does seem to affect mixture at idle.

 

I'm no expert, but I believe that passage provides the atmospheric air source to what can be considered the "enrichment air jet".

For the main circuit, you have the main fuel jet and it's complement, the main air jet. The main fuel jet is in the bowl and the main air jet is in a couple of different locations depending on what carbs you've got, either in the carb intake throat or up under the diaphragm hat.

For the pilot circuit, you've got the pilot fuel jet and it's complement the pilot air jet. The pilot fuel jet is in the bowl near the main fuel jet and the pilot air jet is up under the diaphragm hat.

The way it looks to me, for the enrichment circuit, you've got the enrichment fuel jet and it's complement, the enrichment air jet. The enrichment fuel jet is pressed into the bottom of the hole in the carb bowl and what I believe is the enrichment air jet is a small hole in the side of the enrichment pickup tube very near the top where it enters the carb body.

If you look very closely at the pickup tube, you'll find that there's a small hole in the side of it way up at the top....



And that other hole on the right side in the pic provides a passage for atmospheric pressure air above the fuel in the float bowl to reach the small hole in the side of the enrichment pickup tube. Like I said, I'm no expert, but that's what it looks like to me.

And since the entire enrichment circuit, including that hole, is completely closed off when not in use, it should have absolutely no effect under any condition unless the enrichment lever is being used.

Burnarr