Topic: Fine Tune 1976 400F

[grumpy56]

Have ridden thesem-finished "project" 400 for over 100 miles now and it runs well in every regard except two. (1) When cold the #1 cylinder does not fire until it warms up a bit. Fussing with choke or revving it a bit does not get it to fire. Have rebuilt all the carbs and am about 1.75 turns out on the mixture screw with all jetting per stock specs. (2) When cold, throttle response is perfect. However, when hot, right off of idle is a alight "bog" or non-response. Give it a bit more throttle and it revs fine, but right off of idle is that hesitation. Suggestions appreciated.

[Mark1976]

   So before I get ahead of myself here, lets get a little clarity.
   The ignition is good, plugs, points, caps etc.
   This is a rack you built from 2 different sets to create 1 good set. Correct.?
   If that's the case you're going to have to look a little closer at the entire carb rebuild and
reassembly process, as it's described now your issue sounds like a dirty slow jet or slow jet passageway in the #1 carb. That it improves as it warms is a pretty good indicator of this, as  the engine warms, a slightly lean enough condition in the slow speed circuit will enrichen just enough to fire once its hot.
   The issue with it developing a hesitation once it warms up indicates a rich condition overall, double check your float heights (level). Make sure that you've got good brass and their accompanying o-rings and make sure your needles are in the proper position.
   Then if all of that is good, double check you sync, if its off enough your #1 carb problem could be there, however if its that far off you ought hear quite a bit of primary knock regardless of temp.
   Small carbs like these can be quite sensitive, so everythings gotta be clean and properly adjusted to function as it should.
   

[grumpy56]

Thanks Mark. New electronic ignition, plugs, and carb rack created from two sets of carbs. Plug wires are original. Will go through the things you mention to try to sort this out.

[Mark1976]

   Do a clear tube to check float levels, this rack is quite sensitive to a high float level. Do a bench sync before installing, if your able to get a good sync in on the bench it'll start right up and idle quite nicely, then you can throw on a set of vacuum gauges and get a clearer pic of where your at. That idle issue your having is not uncommon but it normally involves the #4 carb, that's the one carb that is highest when the bike is on the side stand and as a result it's the first carb to go dry and varnish if left for long periods (weeks,months) of time. If your bike has significant mileage the primary chain will knock quite loudly at idle if you have a skip or poor carb sync.

[grumpy56]

Did a bench sync before installation, but didn't use the "tube" method for float level yet. Mileage only 6200 and cam chain is quiet. Carbs are clean.

[HondaMan]

What kind of 'electronic ignition' does it have, now?

[Mark1976]

What kind of 'electronic ignition' does it have, now?

   To hondaman's comment, I've used the dyna and it works but I wouldn't suggest it on the 400f, I've installed the points with hondaman's supplement that eliminates the condenser's with a set of dyna high voltage coils and couldn't be more satisfied. Not quite, set it and forget it, but pretty damn close. Same point set for the last IDK how many years its been so long.

[grumpy56]

Installed this unit from David Silver Spares. Could not get the original plate (with knock-off points and condensers) to time.

[Mark1976]

   Do you have the honda or ngk style of plug caps, make sure they don't ohm out. The early caps were 10 ohm, most now (if your using them) are 5 ohm, but if their old and abused they'll read well in excess of that and that can be a issue as well.

[grcamna2]

   So before I get ahead of myself here, lets get a little clarity.
   The ignition is good, plugs, points, caps etc.
   This is a rack you built from 2 different sets to create 1 good set. Correct.?
   If that's the case you're going to have to look a little closer at the entire carb rebuild and
reassembly process, as it's described now your issue sounds like a dirty slow jet or slow jet passageway in the #1 carb. That it improves as it warms is a pretty good indicator of this, as  the engine warms, a slightly lean enough condition in the slow speed circuit will enrichen just enough to fire once its hot.
   The issue with it developing a hesitation once it warms up indicates a rich condition overall, double check your float heights (level). Make sure that you've got good brass and their accompanying o-rings and make sure your needles are in the proper position.
   Then if all of that is good, double check you sync, if its off enough your #1 carb problem could be there, however if its that far off you ought hear quite a bit of primary knock regardless of temp.
   Small carbs like these can be quite sensitive, so everythings gotta be clean and properly adjusted to function as it should.
 

 

[grumpy56]

don't know what version these are...assume OEM honda

[Mark1976]

   Pretty much. If you get the time, pull each one off of the coil wire and check it w/a volt ohm meter, and while you're at it trim the plug wire a smidge to make sure your getting good conductivity. Some of the early caps will actually have the ohm rating embossed on the cap body. It's an old bike, time takes its toll on everything, ya never know what the previous owner did or didn't do...