Topic: Gutless engine

[Lozscott]

Hi all , I have recently finished rebuilding a 400 , a rusty old mess that had been a winter hack rat bike in a previous life and sat in a damp garage for the last 20 years . I am really pleased with how it looks and it rides and handles well but the engine is gutless and wont rev and makes a ticking rattle on the over run and tickover . I replaced cam chain and tensioner blades , primary drive chain and new set of pistons but i am worried it might be camshaft / head / top end problems , i know the cam lobes were worn to minimum limit . I was wondering if anyone has any suggestions before i start throwing money at the problem , does anyone with experience of these motors live around west yorks or east lancs , it would be a great help if someone could have a listen to it , i am in Halifax , Thanks Loz

[ekpent]

 It certainty is a looker. I am always very impressed with the level of expertise and detail you fellows from England follow doing a restoration.

[jakec]

It certainty is a looker. I am always very impressed with the level of expertise and detail you fellows from England follow doing a restoration.

It looks amazing.. I'm jealous. Did place the Honda stickers a bit high though

[PeWe]

If ignition is set too late, the engine will feel like all power is gone.

I retarded the ignition when engine pinged at take off (too lean pilot jets). Pinging disappeared and so did the power and nice acceleration.

[Lozscott]

Thanks PeWe will re-check timing tomorrow , and give it a compression test as i bought a tester kit at stafford show 2 weeks ago . Yes logo's are a bit high , it took a lot of time and measuring to get them that far off !

[disco]

Check valve clearances as well!

[Terry in Australia]

Well it's only a 400 with around 37 BHP at the crank, so it's not going to shred the rear tyre any time soon, but if it feels really, really gutless, I'd check that it's running on all 4 cylinders. If one of your header pipes is way colder than the others, it'll be that cylinder, and the cause will either be a blocked pilot jet, an incorrectly adjusted valve, or a bad plug lead.

[Lozscott]

Thanks Terry , yes checked the easy stuff , am running ok on all cylinders , valves re checked about 3 times . Just re done timing , 2&3 a bit retarded ( new points bedding in ? ) so slight improvement . Compression test interesting , struggles to 60 psi on No3 , others 70-75 , anyone know what a good compression should be ? Still doesnt want to rev above 6 - 7000 , i thought they were revvy engines . I am sure my 250's were quicker 30 years ago

[disco]

I'm not familiar with the 400/4, but those compression numbers are way low. Did you carry out the compression test properly? Fully open throttle etc?

[Bodi]

With such small cylinders, compression readings change a lot with different gauges and mostly one looks for consistency across the four. But unless your gauge has a very long hose, that sounds pretty low.
The engine should pull happily all the way to redline.
Is your advancer working properly? Confirm that and then set timing at full advance rather than at the F mark at low RPM.

[Lozscott]

Thanks guys , i should have read compression tester instructions more carefully , yes did them with throttle closed , just re done them and now getting 115 psi on No 3 and 120-125 on other 3 so less of a difference now . Re done timing , wow thats a long way out to set it , i just moved timing plate all the way anticlockwise and am 2/3rds the way to advance mark . ( yes advancer works fine ) Just had a quick spin and first impressions are it is revving better ( difficult to open it up at rush hour - will have a longer ride tomorrow ) Is there no down side to setting timing so far from 'correct' setting . Still got the loud ticking/tapping , sounds like a very loud tappet but isnt and plugs look a bit on the white side ( fitted 38 pilots as it wouldnt tick over on 40's --??? )

[carnivorous chicken]

Compression is a bit low but it should run fine with those numbers. Haven't seen anyone mention a carb sync yet so I will throw that in with the other advice.

[Bodi]

It should not be very far from stock setting. What I suggested is to set the timing to between the advance marks AT HIGH RPM - high enough for full advance and a stable strobe image. Do not set the slow rpm timing to the advance marks! That will give you a bad idle and probably massive pinging when riding (will damage the engine eventually). The idle/low rpm advance will be slightly off the T mark but that just doesn't matter. Any actual riding will be at an rpm that has full advance - so set it for that.
With the full-open points gap set to spec (spec not in front of me now, should be easy for you to find) the fixed points should time up within the main plate slots. Then the movable set should be settable within its limited adjustment.
Note that any slop in the points plate so it can move laterally when set in place will make points adjustment rather frustrating. Trying to move the posts in tends to break them off, but temporary shims of anything like plastic or metal between the plate and the locating ears to keep it able only to rotate will solve that.

[754]

Nice bike..
 I got to ask, what is the machine behind it in the first pic ?

[dave500]

if you got a timing/strobe light forget about the f mark,shine the light and watch the marks as you increase rpm,keep revving until the advance stops advancing,dont be scared itll handle it!now adjust the plate to those full advance marks,go to the most clockwise one,set it there,forget where the strobe shows it at idle.

[Lozscott]

Thanks bodi and dave , yes that makes a lot more sense , so i am now just a little more advanced than when i started . motor still doesnt want to rev much above 5000 even in lower gears , i managed to push it to 7000 down hill . I still think plugs look very light ( gray/white ) so am wondering if i should try bigger main jets , the question would be why . I have no snorkle into the air box but have new air filter element and carb rubbers - no leaks there . Anymore ideas anyone for power loss - there may be something very worn in cylinder head

[Lozscott]

Oh , and its a sedgewick planer thicknesser in the back of the picture , half a ton of cast iron probably 50+ years old - great piece of kit !

[Don R]

 The one I dragged home in a downpour had a partially plugged muffler.  After I ran it the first time water seeped out of the pipe, later when I ran it around the neighborhood it got louder and now it runs a lot better. It had also been owned by older folks and probably hadn't seen the upper RPM's in years. It's running in nicely now.
 Good luck with yours.
 ps, my brother bought a 500 and as the original gas runs out and is diluted with fresh it gains more power and rpm's.

[Terry in Australia]

Thanks bodi and dave , yes that makes a lot more sense , so i am now just a little more advanced than when i started . motor still doesnt want to rev much above 5000 even in lower gears , i managed to push it to 7000 down hill . I still think plugs look very light ( gray/white ) so am wondering if i should try bigger main jets , the question would be why . I have no snorkle into the air box but have new air filter element and carb rubbers - no leaks there . Anymore ideas anyone for power loss - there may be something very worn in cylinder head

You mentioned that you replaced the air filter mate, did you replace it with an original Honda one, or an aftermarket item? I've got a K&N filter in the airbox on my CB750, and because they flow so much more air than the restrictive OEM paper filters, they cause the stock carbs to run very lean, so I'm up to around 140 main jets at the moment. If you've still got your old filter, swap them and see if it makes a difference.

[PeWe]

I used 147.5 mains with conical pods.
Mikuni jets in stock CB750 carbs, needles 1 step richer. 836, ported head, cam, rather open 4-1.

[ozpacman]

I'm wondering if you may have inadvertently got your valve timing out by being one or two teeth out on the camshaft sprocket when the new cam chain was fitted?

[Tim2005]

Sounds very much like this 400's problem, which was down to incorrect valve timing  http://forums.sohc4.net/index.php/topic,161126.0.html

[Lozscott]

Thanks for those last 2 replies , i agree that it sounds just like the post Tim referred to . I will be very happy if it is ( and embarrassed ) but it will save many hours of messing with carbs . It has to be something fairly major for such a large powerloss , not a tuning issue . A friend suggested using higher octane premium fuel so was wondering all you guys use . Am running OEM paper air filter and standard 75 main jets , was going to get 80's but will hold on till i have had a check of that cam . Sadly i wont be able to have a look for a week or so due to work but will post back when i have , thanks again all

[Lozscott]

I am going to start a new thread on this(make things quicker)please read ' wrong camshaft ? '