Pilot jet

Hi,

I have an xj650 maxim, 1981, US model imported to the UK.

I bought the bike seized, and whilst waiting for rebore I have stripped and cleaned the carbs.

Let me say I am a self taught home tinkerer, not a professional mechanic, but have kept a variety of machines large and small going over the years.

Over the years there have been a few bodges to this bike, and I don't trust any previous work, there is evidence that the carbs have been apart before.

I bought a rebuild kit for the carbs, which obviously fits more than one type of carb, as there are far more bits than needed ( jets 2x112, 2x122, 2x43, 2x40, pilot jet, quite a few o-rings etc).

So, here's the question, in the manual the pilot jet is "rocket " shaped, in my carbs it was the same shape as all the other jets, like a grub screw with a hole through it.

I tried the new rocket shaped pilot screw in the pilot hole, and it doesn't go in far enough to engage the screw thread.

I have replaced it, like before, with a standard jet, did some carbs have grub screw type pilot jets, or am I missing something?

I measured the old jets as they are not marked, and have used 112 main, and 43 pilot.

I obviously have no idea how this bike was running before, but not using the rocket shaped pilot jet is bugging me.

Thanks in advance for your thoughts.

 

If it isn't like the one you took out don't use it. The last think you want lto do is screw up the threads in the pilot system. Contact Chacal for the right kits.

 

Thanks tabaka,

I agree, and have used like for like jets, just intrigued as to why the diagram shows a different type of jet.

Maybe an earlier carb.

 

Hitachi carb? The air jets (on top of carb) don't have the top flange like the Fuel jets do (bottom of carb on float bowl side). Air jets look like the grub screws with a hole. Is that what you are saying? None of the jets in either of the 2 carb kits I was given by the seller were for air jets, they were all fuel jets.
There is also a write up about carb threading for pilot jets changing one year.
When I needed to put in different air jets to bring my carb to stock specs, I had to get individual ones from xj4ever.com

Maybe you should post some pics for clarity. That always helps
Just put the pics on a post it then write on the post it what each one is (original from carb, from carb kit, found in a cracker jack box etc)

 

I will do that.

The air jets at the top of the carbs are under a plate, and didn't come in the kit, they weren't clogged, so cleaned and used again.

My manual states Hitachi, but there is nothing on the carbs to say this, so I take that with a pinch of salt.

I will photograph the jets later.

 

Here are photos of my carbs.

The jets are the ones that came out, the replacements, and the rocket shaped pilot jets I expected to use.

That's the bit I am making sure is right, can pilot jets be grub screw type?

Engine needs reassembling before I can try it!!

 

Although I'm a noob to this bike, rebuilding the carbs is fresh in my mind after spending a few weeks reading/watching/doing it.

In your photo, those are fuel jets. On the right is the pilot mixture screw/needle.
IN Photo 2/3 Those fuel jets look backwards in your labeled installation unless the camera is playing tricks.
Main jet (center with the copper crush washer) should be larger than the pilot fuel jet.
Its the opposite for the air jets (under the plate on top). (note that if you have the service manual, the photo shows the right ones, but the labels are backwards xj4ever.com mentions this)
For me, I cleaned and reused every jet that was to spec, then replaced the ones that were not. I also used the original aluminm pilot mixture screw & spring but used the rubber o ring from the kit.

Did you get the little plunger/needle that goes on the bottom of the float? Also, did you remove the brass fitting it fits into to replace or at least clean out the screens under it?
Mine was all full of crud. Also, I have seen plunger/needles in Ebay/amazon kits that do or do not have a rubber tip. I got the rubber tip ones in my rebuild kit from Len at xj4ever cause I did not trust the non rubber tip one.


http://xjbikes.wikidot.com/carb-specs

Years & Models: 1980-1 XJ650 Maxim, Midnight Maxim, and XJ650RJ Seca USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 4H700
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-10
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

 

You are so right, I have got the pilot and main the wrong way round!

I have replaced the strainer gauze.

Now I didn't remove the mixture screw, Haynes manual warned against removing it, no idea why, but I will now replace it.

I had assumed the item on the right was a pilot jet, and didn't consider the mixture screw.

You have answered my question.

Thank so much.

 

watch the mezzmo engineering carb rebuild youtube video. It is a wealth of information.
it goes over reinstalling that mixture screw.
read the threads here and xj4ever about church of clean. There is WAY more to carb rebuilding than opening it up and just replacing a few parts.
There is a spring, then washer, then O ring. Use a new o Ring from your carb kit. Its the tiny O ring in the kit.
I used a cut off dental pick to pull the old O ring that on all my carbs stayed inside the carb when pulling the mixture screw.
There are 2 passages that you MUST make sure are clear. The bowl enrichment passage is covered in the mezzmo video, but there is a test to verify the Pilot fuel jet to pilot outputs (there are 3) on the carb body.
There is a video where you put the mixture screw in w/o the O ring (carb spray can eat the o ring). plug the air jet (I just took a toothpick or broken off q tip) then spra carb spray into the pilot fuel jet (remove the jet).
BOTH those passages were blocked on 3 out of 4 carbs until I sprayed them clear. Even after stripping all the way down and ultrasonic cleaning. If those passages are not clear, don't count on your choke/fuel enrichment to work well.

BTW, I scored an additional Hitachi carb set for $110 shipped. Stripped bowl screws and a couple missing jets, but that is nothing compared to what I got. I'm going to rebuild this in my spare time (not that I have spare time). So I have a spare carb set. If I have a spare, I'll never need it

 

That's very useful.

I have had another look tonight, I had put the main and pilot jets the wrong way round in that one carb, doh! Good job I chose that one to photograph.

The o-rings were missing from the pilot air screws, whoever had it to bits last didn't get it quite right, which means I don't trust replacing things like for like.

The ports in the bowls are still soaking, completely blocked, lots of carb cleaner and jiggling with fine wire hasn't worked yet, unfortunately I don't have an ultrasonic cleaner.

 

double check the o rings in the pilot screw hole. Use flashlight and make sure. You definitly need an o ring and you don't want 2 of them as that makes it richer than the # of turns might dictate.
Just don't get a wire stuck in the hole in the bowl. I had to soak and pick

 

Buy one. It’s the only way. Even then you might need a compressor and blow gun.

 

An ultrasonic cleaner has been on my wishlist for a while, I have a compressor, which has lots of use for air tools.
I finally cleared the enrichment ports in the bowls, 2 cleared after just ( 2 days in carb cleaner, regularly changing the cleaner) soaking and agitating with fine wire, 2 were stubborn.

The method I finally used needed caution, with carb cleaner in bowl, heat the bowl, the cleaner will ignite, let it burn for 30ish seconds, extinguish by covering, agitate.

Worked for me, all 4 now blow through.

Valves relapped, and stem oil seals replaced, it's now dangerously close to engine reassembly!!

 

Here is the pilot jet test video I spoke of.
Again, don't do this with the pilot jet o rings installed.

 

I just thought I'd give you helpful people a quick update.

Engine is back together, and she started first press of the button! That surprised me!

On the down side, running way too rich, gulping fuel, and puffing out loads of sooty smoke, plugs lovely and black - just waiting for smaller jets to be delivered.

Going to start on replacing fork seals and grease steering bearings whilst waiting for jets.

 

Congrats.
Fuel Enrichment/Choke cable set up right?
I found that I had to adjust the position on the clamp at the top of the carb.
I have mine set up so that then my choke lever is all the way to the right, it has let go of the bottom of the choke by about 1/2 mm if you don't see it let go enough, loosen the screw where the cable sleeve end is held on to of the right of the carb and then push the cable sleeve end closer to the carb.

 

The choke cable isn't attached, when I bought the bike it was tied to the actuating lever as the inner cable was too long!

Obviously the wrong cable, I plan to shorten the inner cable and attach a new nipple.

I held the choke open manually to start it, and all 4 plungers pop down nicely when the actuating lever is released.

Your advice on cable set up will be useful when I come to attach it.

 

I just re-installed my choke cable, but the thumb control at the handlebar seems to be springing back instead of holding the choke open. I know prior to this, it held fine..so I could open and close as bike warmed up.

 

I thought I would give all you helpful people an update.
Bike now on the road and running really well.
Really powerful engine and good handling.