New member, non-running 84 Maxim 400, Wish me luck.

Have you checked the timing? It's electronic so there's not too much to adjust...and I am a points guy, so I con't tell you how to do that, but when I hear backfire, I start thinking about timing.

I don't think the float valve is likely to be the problem with at least getting it to fire correctly, but it could be an issue with getting it to run smooth down the road. I wouldn't worry about it at this point unless gas is overflowing.
 
No I have not checked the timing.

Would you say I am getting close though? The other day I was just happy to have power. Now I am getting some combustion, although not the way I would like.



TrueG
 
In looking at the service manual, it appears that I also missed the pilot jet. Would a clogged pilot jet cause backfiring through the carbs and out the air intake?
 
Well since backfiring is often caused by a lean condition, I am hoping that cleaning the carbs will correct the issue.

Last night I picked up some Pine Sol and dropped my carbs in for a nice little bath.

Today after work I will clean them off and take a look.



TrueG
 
The carbs came out nice and clean and I was able to blow through the main and pilot jets.

I put it back together, but it still wouldn't go. I get the occasional backfire and I feel puffs of air coming out of the exhaust.

I guess timing is the next thing? How do I check the timing when the bike doesn't run?




Thanks,
TrueG
 
what about all the other orificies of the carb?

1 in the float bowl and one travels to the pilot system at the front!

float height set correctly (26mm on brass floats)
 
I checked the Main jet and pilot jet at the bottom (I was able to blow air through each, although slower through the pilot jet due to the smaller hole). I checked the Pilot air jet at the intake side. The float pin was nice and springy. The passage from the bowl to the intake was also clear.

I didn't mess with the floats.

I see other posts with similar starting issues that relate to the pick-up coil. I wonder if this could be related?
 
OK, well I got the bike started after putting the original spark plugs back in. Interestingly, the plugs that came with the bike are D8EA (left) and D7EA (right). The sparks plugs specified in the manual (and the plugs I bought) are DR8ES-L, but after putting the originals back in it fired right up.

It's actually running really well (smooth idle). I must have a stuck float though because gas is coming out of the air intake after idling for a short while. :(
 
Measure the floats before concluding they are becoming stuck. Also inspect how far the float needles drop when the carbs are held right-side-up. I have solved flooding issues on more than one bike by adjusting the float needle travel. Often when people bend the tangs to adjust float height they inadvertently bend the tang that adjusts float needle travel.

Did you remove all of the jets when you blew air through them, or have they all still been in place? You must remove them in my opinion; many have tiny holes drilled laterally through them that easily become clogged and don't forget the emulsion tube.

I still suspect all of your problems are carb-related; especially since you're flooding. Was the gap on the old and new plugs you tried different?
 
I can't remember the exact gap of the old plugs. The new ones were factory gapped to the correct distance (0.023 – 0.028″).

Ya, I will have to check the float distance when I get home from work. I may also have to get in there and do a better job cleaning those jets. :(
 
I spent weeks tinkering with these carbs. I came up with all sorts of cockamamie theories about what could be causing problems. In the end it was cleanliness of carbs, the cleanliness of the fuel entering the carbs (rust), the float height, or the foat needle travel. Do it once and do it right or you'll end up like me; Ive taken them off so many times I can pull them off, change jets, and have the bike running again in 5 minutes :)
 
Doh! My bad, it wasn't gasoline.

Today after work I pulled the bike out on to the drive way, into the sunlight. I started it up and looked in to see if I could tell where the fluid was coming from. It was then that I noticed the smaller hole below the carb intake. I followed the hose and found that it led to the crankcase.

I hadn't changed the oil since I got the bike as I was going to do it after I got it running. Anyway, there was way too much fluid in the crankcase and it was being blown out the overflow. I changed the oil and now it runs great, with no leaking fluids. :D

I think I will need to rebuild the petcock though. When set to 'on', it feels like the bowls are not filling fast enough. Also there is a slight drip when the petcock is set to 'on' and the hose if off. There is no hesitation or lack of fuel when set to 'pri'.


TrueG
 
The bowls will fill faster if you adjust the float needle travel; if you allow them to open too far, however, you'll get flooding because at a certain point they get stuck open. I used the universal petcock from partsnmore without any issue so far.

If you have no problems when on prime your vacuum hose probably has a leak. You could leave it on prime, but remember to shut it off when you park the bike. The hose goes from the petcock to the carb boot; this is probably where the leak is.
 
Welcome to the Forum I'm also a Maxim owner I have the 650 though it's called the Yamaha XJ400 or XJ650 it's not an XS and there are alot of mechanical differences but overall is the same bike the guys on here are great. If you have any XJ questions let me know I
ll see what I can do I'm jsut learning the mechanics myself but I'm coming along really well on my MAxim
 
That isn't your only problem. You are probably off riding it right now, I'm late as can be. It sounds like possible timing/ syncing problems.
 
Since getting the bike running I was able to locate another 83 Maxim 400 in the area for sale. It didn't have papers, so the guy let it go for $150.

I have been able to pull a bunch of parts off including the handle bars, mirrors, clutch lever, gas tank, front and back fenders, horn, cables and screws.

Here are some pictures of it now.....
IMG_0494.jpg


IMG_0493.jpg


IMG_0495.jpg


TrueG
 
Last week I pulled the carbs off of my parts bike and cleaned them up. Instead of using a proper float bowl gasket, the previous owner used a bunch of instant gasket goo.

I was able to find some gaskets at a great price at Part N More. I also purchased a new air filter and mirrors from them.
http://www.partsnmore.com/

Anyway, I cleaned them all up, put them together with the new gaskets and swapped them for my old carbs.

They seem to work better in that the choke seems to work (although it brings the idle up really high) and it doesn't seem to jerk as much when I let go of the throttle.

The problem is that now I have backfiring/misfiring out of the right exhaust pipe.

Does that make sense at all?

Thanks,
TrueG
 
did you put the right main jets back in? each side is different by 10 sizes or so. Also, run D8ea plugs. They work great and are about $1.58 each at Advance Auto or the like. Are you running a stock airbox? And what filter are you using?
 
Yes, everything was put back together correctly. I've disassembled these carbs probably 6 times (between the two sets).

It was backfiring/misfiring while idling and under power. Everything is stock except for the paint job. The air filter is new (OEM).

The plug situation is interesting. My bike came with one DE8A and one DE7A plug. My parts bike came with two RA6HC plugs. The manual specifies DR8ES-L so that is what I bought.
 
This evening I put my original carbs back on. The backfiring/misfiring is gone.

The only problem I have with my original carbs is that the bike seems to jerk and slow down too fast when I let go of the throttle. I have no problem with power and it doesn't jerk in neutral. Only when it is in gear.

I was hoping the new carbs would correct the problem. And they seemed to, but obviously the backfiring/misfiring is a much bigger issue.

Does anyone know what I am describing? Sometimes in a car with a standard transmission, if you go into first and get up to high RPMs and let go of the gas is jerks and slows down really quickly. My bike does that, especially at high RPM.

TrueG
 
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