Topic: 400F Do I have to run it at 7000rpm?

[gregk]

I took my 400F to a bike rally in Riondel BC this weekend.  This was the first outing for the bike since a partial rebuild/restoration last winter and I was very curious as to how it would run on the highway and what kind of range I could get out of a tank of gas. 
On the way over I was travelling  with a friend who has an 350 Eatons Road King.  He travels about 55 mph so it was a relatively slow trip.  The Honda seemed to lug in 6th and at times I had the throttle wide open with little or no response.  This makes me wonder if the bike needs to be driven on the high side of  the tach.  I could easily shift down to 4th gear at this speed but the bike runs about 7000rpm.  I am used to the relative power of my 76 750F and just thought that I could cruise at 60mph in 6th gear with the 400. 
The range question on the tankfull is approximately 78 miles before the reserve. 
I am wondering if these observations are true to this bike? 
On the way home from Riondel, I ran about 65 to 70 mph but any little change in grade requires a downshift. 
Is this the way these bikes are? 

Greg

PS  There was a Norton Rotary at the rally.  Owner claims to have the only one in Canada

[Tim2005]

400f's often have a flatspot around 5500-6000 rpm, but I sense yours has a problem as 78 miles before reserve is shockingly bad. My stock 400f gets around 115-120 miles before reserve, even my much modified 460 manages over 90. Are your plugs black?

[GroovieGhoulie]

I've never had that problem with mine.  I can get 120ish miles on the tank before needing reserve.  More if I am easy on the throttle.

The "lugging" should also not be there.  Mine'll cruise all day in top gear, even down to 35-40mph and pull away cleanly when I open the throttle.

True, a bad headwind or grade will have me stirring the gearbox, but only down to fifth.  Passing power means I'll drop a gear or three depending n how quickly I wanna go.  To ride these bikes quick and keep the engine on the boil, takes an intimate knowledge of, and frequent use of, the gearbox. 

You CANNOT ride the 400 by just twisting our wrist.

[Gordon]

Is anything changed from stock?  Air filter, exhaust, sprockets, etc?

[gregk]

The bike is stock everything.  There is definitely a flat spot or no response when in a higher gear at low rpm. 
I have done nothing to the bike other than take it apart last winter and repair a few things. 
When operating at a low rpm and opending the throttle it seems to "bog" and won't increase engine rpm.  As I haven't had a lot of saddle time on this bike, i am unsure what to expect but so far I am not impressed.  I thought I would get performance like you speak of and gas mileage. 

Greg

[TwoTired]

Are all cylinders firing?  Are the head pipes even temps?

If the carb slow system is gummy/dirty/blocked, you can get those symptoms.  What is your air screw setting?

When was your last complete and thorough tune up?

How old is your air filter?

What do your spark plug deposits look like?

[gregk]

TT

When I had the bike apart last winter to put a helicoil in a plug, I cleaned the carbs and unfroze the cam chain tensioner.  The air filter it new as are the plugs, points, condensors. 
What is included in the slow system of the carbs?  Will check plugs tonite.
All cylinders are firing and air screw is 1.5 turns.

Possibly didn't get the slow system of the carb cleaned.  If that is the case, i don't look forward to removing the carb bank again.

Greg

[Gordon]

TT

When I had the bike apart last winter to put a helicoil in a plug, I cleaned the carbs and unfroze the cam chain tensioner.  The air filter it new as are the plugs, points, condensors. 
What is included in the slow system of the carbs?  Will check plugs tonite.
All cylinders are firing and air screw is 1.5 turns.

Possibly didn't get the slow system of the carb cleaned.  If that is the case, i don't look forward to removing the carb bank again.

Greg

The performance you're describing is definitely not that of a good-running stock 400F.  How have you verified that all four cylinders are firing? 

With the engine cold, start the bike, and while it's idling, feel the header pipes to see if they all come up to temp at about the same rate.  If one or more is colder than the rest, then you probably have some clogged idle circuits. 

Basically most everything else that could cause your problems are checked and adjusted during a regular tune-up.  Stick with it, you'll get this figured out!

[TwoTired]

What is included in the slow system of the carbs? 

The slow circuit is primarily active while the slides are near closed.  But, they do contribute at other slide settings, too.  Mains/throttle valve metering is set with this contribution expected.
The slow circuit is comprised of: the air screw, the slow jet, the slow air jet, the feed hole into the carb throat, and, of course it's very own passageway drilled in the carb body.

All cylinders are firing and air screw is 1.5 turns.

The roll on throttle response can be improved by closing down the air screw to make the idle mix richer.  (this assumes clean idle circuits)

I've had slow circuit clogs that only allowed the head pipe to get hot when the throttle open opened up.  Something to check for, anyway.  Note that for your bike, choke opens the throttle, too.

Possibly didn't get the slow system of the carb cleaned.  If that is the case, i don't look forward to removing the carb bank again.

Reminds me of the old adage:
A job worth doing, is worth doing twice!
 
Cheers,

[LoopsAndLogic]

It sorta sounds like what I had. Bogging and no pickup at all in the top gears.

So with my knowledge on carbs, I presumed it was the needle jet, cause it handles the rpm range from 3750 to 7000 rpm.

I popped the clips 1 notch down for a richer mixture, and put it back together. BOOOOM!!!

Instant acceleration!! Though, I did have to adjust my air screws to 2 full turns out, cause the lowend was hesitating due to the richer mixture.

Hope you find the problem. And just a word of advice, if you do plan on running the 400 up in those high rpm's, do have some extra head gaskets. As the OEM's were prone to leak with high mileage.

Me, 22k with a leak and still running strong

LL

[gregk]

Checked the header pipe temperature last nite.  All pipes seem to get hot or rather none hotter than the others.  Pulled the plugs, three are light tan and one sooty black. 
The bike idles as it should and seems to rev freely when on the stand.  The trouble starts when the bike is put under a load. 
Any other thoughts?

Greg

[gregk]

When I had the motor out of the bike, I had the float bowls off and took the jets, needles and seats out to clean.  I didn't take the slides out as I am positive that I am the first one to open that motor since it was built.  Right or wrong, all the floats were the same height.  The carbs still have the yellow paint intact which I believe was applied at the factory for some quality control measure. 
I have backed off the air screw on # 4 to see if I can get a better burn on the plug. 

Greg

[malcolmgb]

have you checked your ignition timing, sounds as though it may be retarded, always a good idea to go back through everything not just concentrate on carbs.

[gregk]

Previously I was having an issue with the timing.  Went through a problem with the breaker plate not being centered in the bosses of the crankcase.  Got that solved by shimming the plate, adjucting the gap then the timing.  Still could not get the timing to hit the full advance mark.  I had set the gap at the minimum.  I would like to try a happy medium and see if this makes any difference. 

Greg

[Cvillechopper]

I had that exact plug reading on a friend's 750 when we first got it running.  Turns out the PO hadn't tightened the main jet in properly and it fell out.  Not knowing the particulars of your carb set-up, drop the bowl on the offending cylinder and take a look and the main jet seating.  You should be able to do this with the carbs on the engine.  I'd also check the seal around the jet.  One way or another, you're getting too much gas to that one cylinder.
It's not a timing thing or you'd have 2 cylinders off.  

Good luck.  
James

[gregk]

Boys

I sent back to the timing.  I had set the point gap at 0.012 and could not get the advance timing marks to come anywhere near the mark.  Last nite I set the points at 0.016 and retimed the bike.  Wonder of wonders, I can now get the advance marks to line up.  The only change being the point gap. When the gap is 0.012, I think that the bike's timing was retarded and therefore would get crappy performance and poor fuel economy. 
So as I am doing this, I can see a storm commming over the mountains and before I finish in the garage its blowing sideways.  Now I'm thinking well, I'll just get up early and take the bike before work for a run to see if my timing has helped the performance.  Immediately after this, the power goes out and is still out! 
I am going to assume the best and thank all of you who have given me their thoughts and advice.

Greg