Maxim 400 help Please!

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User9053

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Hey everyone, here is another thread about having problems with an XS400 :doh:

Anyways i'm having 3 major issues.

1. No power below 2.5k
2. Slight hesitation at around 7k
3. Coughing and no power @ WOT (no matter the RPM)

I had the carb ultrasonically cleaned as I was having worse issues with low rpm power below 3k but the clean at least made it a bit better (2.5k) and its ridable but sucks if I have to start on a hill.

The jets in there were 127.5 (probably jetted from PO) so today I changed them to 135 and it seems to run a little better. Midrange is perfect, plenty of power but the low end power still sucks and slight hesitation at 7k and no power at WOT.

I tried to do some testing thinking I may have put too bigger jets in by first removing the airbox door, then removing the filter and taking it for a ride (simulating higher air flow and leaning mixture) both instances it ran worse so i'm thinking bigger jets??

The pilot needles are set at 3.5 turns and i've played with almost every setting and it seems to make not a lot of difference to low end power. Plugs look on the lean side, slight white flick on the electrode arm mostly white .
 
Last edited:
Have you checked the valve clearances? If not, so that first. Then adjust the Pilot screws for a good idle and sync the carbs. Then follow the tuning guide found here.

BTW, that is a nice looking Maxim! How do you find the header and muffler sound? Obviously louder than stock, but is it annoying? There are a couple of us considering the MAC system...
 
Pipes are good, very loud but not annoying. Friend has a Maxim 650 and my bike sounds meaner lol.

Is there a guide anywhere for doing the valves? Thanks
 
The procedure for checking and adjusting the valve clearances are in the manual. If you haven't got one, it can be found in a sticky post at the top of this section entitled "Yamaha XS400 Manuals". Be sure to get the DOHC manuals, they are for a Seca but will cover 98% of your Maxim.
 
Im thinking I need to go up pilot jets for the low down bog. Can anyone recommend a size and the stock size?
 
Ok so I got further with my problem. Pulled the carbs apart again and using that guide I lowered the fuel level in the bowls but didn't make a difference. When I had it apart I checked the pilots and realised they are bigger than stock 42.5, so I tightened up the pilot screw and got more power down low! Currently in at 2 turns out and it seems ok. So I'm thinking the combination of lower bowls and tighter pilot screws may have slightly fixed the low end. I put my old jets back in 127.5 and it's better but not at WOT. Still stumbles and such. Should I go lower? Should I stagger the jets as I'm still running the stock air box? Thanks
 
Still sounds lean at WOT, I would not go any lower on the mains. What air intake system do you want to keep? Adjust your carb with the intake you want, don't adjust the intake to the carb..... I hope I'm making since here.....Do you have adjustable needles? Only 2 turns out on the mixture screw would be minimum, I'd think you should be 2.5 or 2.75 out with the correct pilots.
 
I'm going to stick with stock airbox. Don't want to reposition the battery. This thing is the power at WORK was worse with 135 jets and better at 127.5 so logic would suggest to go lower. Because they stagger the jets as the battery restricts the airflow on one of the carbs in thinking maybe only one is running rich??
 
Yes your correct. I'm finding it hard to find a clear guide how to check it. I've looked at the manual but it doesn't make a whole lot of sense to me :-\
 
Ok so I've done the valves and it runs a little better. I noticed that you guys all seem to talk about TDC etc when doing valves. The manual on this site doesn't mention anything about that nor does that link that was posted. Did I do it wrong? It just has a pic of the can lobe opposite to the shim when measuring. Thanks
 
The manual mentions LT or RT marks on the stator behind the left side engine round cover. These marks indicate TDC for the respective side of the motor; left or right.

Oops. You have a maxim. Let me make sure this even applies.

Edit:

This is why you're confused, for the same reason I was. Most of the valve clearance advice you're seeing is for the SOHC motor, not the DOHC like yours; they're different.

The way the manual mentioned is correct for you; you're rotating the motor until the cam lobes are in a particular position. That's what you use as a reference.
 
This bike is similar to my xj650 in valve adjustment. It is important to take your time and make sure the lobes sit entirely upright (with the sharp end pointing to the sky). It is also important you rotate the motor ONLY in the advised direction. Never rotate it back the other direction, because it will lead to poor valve adjustment, because it introduces slack to the cam chain.

It's a bit more tedious than sohc - but totally doable. Good luck! And great looking bike.
 

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