From: noreply on 16 Aug 2007 19:33
Will carbs from a 1982 XJ650 work on a 1982 XJ650? Is the carb body the
same? I figure I need to check all the jet sizes and so forth...
From: noreply on 18 Aug 2007 10:27
Sorry about the typo - I meant to ask if XJ750 carbs would work on a XJ650,
and if the carb body's are the same.
I have a XJ650 that I can't get to start well. I've cleaned the carbs
numerous times. I know it is the carbs, because I have put a set on from a
friends XJ650 and it ran great. I am looking at a used set of XJ750 carbs
on e-bay and was wondering if I could use those.
From: Albrecht via MotorcycleKB.com on 18 Aug 2007 12:28
>I have a XJ650 that I can't get to start well. I've cleaned the carbs
>numerous times. I know it is the carbs, because I have put a set on from a
>friends XJ650 and it ran great. I am looking at a used set of XJ750 carbs
>on e-bay and was wondering if I could use those.
Well, it sounds like you might have some gum and varnish in the idle ports
I won't go deep into telling you how to clean those passages out, because
I've typed it out a few hundred times and posted it in rec.motorcycles.tech.
What you need to know is that the starting enrichener won't work unless the
throttle butterflies are almost completely closed. And, if you have dirty
passages inside your carbs, you have probably turned the idle speed knob to
get the engine to idle.
So, you've unknowingly sabotaged your carburetors.
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From: noreply on 19 Aug 2007 09:50
Are you up for a challenge??? I just can't seem to get my current carbs to
work. I have put close to a couple hundred hours of labor into them. I
think some evil spirit has cursed them. Any help or further advice would be
Here is what I have already tried:
==Thoroughly dismantled and cleaned the carbs three times (details on how
==I borrowed a different set of carbs from a friend who has an `81 650. I
cleaned them for him (part of the deal), and put them on my bike, and then
it started and ran great, perfect. Because of this, I am pretty confident
it is a carb problem. As near as I could tell, his carbs were identical to
mine (jets, etc.) and had the same model number on the bottom of the carb
bowls (both were Hitachi, model 5N8).
==When I clean my carbs, I take them completely apart, except for the pilot
screw set (as described on the XJ CD set, see below). I do not dismantel
the rack, I keep the four carb bodies bolted together. Each time I soaked
the carb bodys in part cleaner for 12 hours. Blew compressed air through
all passages, replaced pilot and main jets with new jets (first time only).
I've paid special attention to the bypass valve and passages. The inside of
the carbs are spotless. I even boiled the carb body and bowls at the
recommendation of a friend. They are very clean on the inside.
==When I clean the carbs, I can't get the �pilot screw set� out. From what
I have read in the XJ CD's, this is three parts below the pilot jet. How do
I get these out? Do I need to take them out? I've tried toothpicks, a
jeweler's screwdriver, and compressed air, but can't get them out. Any
suggestions??? Do these parts screw out, or is it just held in by the
o-ring? The �pilot screw set� consists of a washer, spring, and o-ring,
correct? If these were dirty, would they cause the problem as I described?
==Checked for air leaks by spraying starter fluid around the intake
manifolds and boots (did not increase idle). Because it did not increase
the idle, and my friends carbs worked, I don't think it is a vacuum leak.
==Replaced the air filter.
==Synchronized the carbs with a vacuum guage, on the bike.
==Set the fuel mixture on the carbs with a "colortune" spark plug.
==Once started, the bike idles and runs beatifully, very smooth. Just won't
start when cold without a small amount of starter fluid sprayed into the
==I have the original owners manual, service manual, and XJ CD set, and have
researched them thoroughly.
==I've checked the float level.
==I've checked the tank for rust, removed the rust, etched and coated it.
==Installed a fuel filter.
==Replaced the fuel line.
==Checked the fuel petcock.
==Had it at the local bike shop, they gave it back to me unfixed after 5
weeks, not fixed.
==The local bike shop checked the compression and said it was 120, 120, 130,
140. Is this high enough? I have been assuming since it ran OK with my
friend's carbs, it is high enough.
==Posted in various newsgroups before and got lots of feedback about fuel
additives. Tried two. Ran through a tankful. Also tried getting up to
about 60 MPH, pulling in the clutch, dropping it down 2-3 gears, opening the
choke wide open, and popped the clutch (to create vacuum and suck any debris
out of the bypass valve openings. �I don't think fuel additives are the
From: Albrecht via MotorcycleKB.com on 19 Aug 2007 10:57
>I think some evil spirit has cursed them.
Too much drama.
>==When I clean the carbs, I can't get the “pilot screw set” out. From what
>I have read in the XJ CD's, this is three parts below the pilot jet.
From what I can tell by looking at the online parts diagram (which doesn't
show the idle mixture screws at all) they are on top of the carbs, under a
metal plug that has to be drilled out.
There's an aluminum sprue sticking up, just forward of the diaphragm cap. Is
there a round metal plug in the sprue?
To remove the brass plug, you have to drill a pilot hole, taking care not to
hit the top of the idle mixture screw.
Then screw a small sheetmetal screw into the plug, and pull the screw and
plug out of the hole with a pair of pliers
>I get these out? Do I need to take them out? I've tried toothpicks, a
>jeweler's screwdriver, and compressed air, but can't get them out. Any
>suggestions??? Do these parts screw out, or is it just held in by the
>o-ring? The “pilot screw set” consists of a washer, spring, and o-ring,
>correct? If these were dirty, would they cause the problem as I described?
If you can see the end of the pilot screw, it has a slot for a common
The pilot screw adjusts the flow of fuel/air mixture through the single idle
outlet port that is all by itself. The other three outlet ports are by the
throttle butterfly, they are the transition ports that allow extra fuel air
mixture to flow when vacuum decreases as the throttle is opened.
But you need to get the pilot mixture screw out of the hole so you can clean
out the single ide outlet port. The engine will never idle correctly if this
port (and the passage feeding it) is plugged.
>==Once started, the bike idles and runs beatifully, very smooth. Just won't
>start when cold without a small amount of starter fluid sprayed into the
The single idle mixture port is probably plugged and your engine is idling
off of the three transition ports because you have opened the throttle
butterflies a little bit by turning the idle speed knob up.
Doing that defeats the starting enrichener. It needs all the vacuum available
so it can suck gasoline out of the float bowl.
>==The local bike shop checked the compression and said it was 120, 120, 130,
>140. Is this high enough? I have been assuming since it ran OK with my
>friend's carbs, it is high enough.
It's low, but the engine will run if it has 90 pounds of compression. It just
won't have any power. I would do a valve job and re-ring an engine that only
had 120 to 130 pounds of cranking compression, but the bike would have to
look nice before I would bother with it.
>== Also tried getting up to
>about 60 MPH, pulling in the clutch, dropping it down 2-3 gears, opening the
>choke wide open, and popped the clutch (to create vacuum and suck any debris
>out of the bypass valve openings.
Now that was a bad idea. The idle mixture ports are tiny, and if they are
plugged up, engine vacuum will not suck the gum and varnish out, you need a
strong solvent under pressure or ultrasonic cleaning.
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