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Discussion Starter · #1 ·
I bought this bike a couple of weeks ago and it wasnt running good but i got a good deal on it.

I adjusted the valves cleaned the carb and adjusted the cam chain and installed uni air pods and changed the oil and filter. There was new wires and plugs on the bike when i bought it so i didnt change them but i might now since the bike isnt running good.

I had a question when adjusting the cam chain.....there is a dot on the rod that adjusts it but u can keep on turning if u really wanted it....it looks like it just turns a spring inside that pushes the tensioner....if u turned it 360 degrees would it mess the timing up of should i just make sure that the chain is tight and consider it done...i have checked to make sure that its timed right but i might do that tomorrow....

i couldnt fine jets locally without ordering them and i knew i would need richer jets so i open them up a hair with jet drill bits which i know isnt the proper way to do it but i figured it would get me close enough to hear it run better then i could fine tune it after.
I tried to start it last night and it wouldnt start with the choke on but i took the choke off and it kinda started. I kicked it a couple more times with the throttle open and i got it to run at almost WOT for about 5-10 seconds at around 4k rpms then it dies....i sounded like one cylinder was firing ok and the other one was having a even harder time running.....it was puffing out dark smoke like its running super rich which i can see why it wouldnt fire with the choke on if thats the case.

Its a 1978 honda hawk II CB400t with 16k miles
what should the stock jets be and what do u think they should be with the air pods and it has some kinda 2 into 1 aftermarket exhaust...not sure the brand but its pretty loud.

any help would be great cause i want to get it done so i can start on a 74 cl450 i just picked up
...

i live in upstate NY 600-1500 ft above sea level
 

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First off, welcome to the forum. It's always nice to see another 400 show up. We may be the red-headed-step-children in the vintage Honda Twins family but the folks here still treat us nice. ;)

The jets in your 78 should be 75 primary and 110 secondary. If you search the forum there was recently a discussion about jets and what the sizes equate to. Also some links to places you can buy jets.

It does sound like you're running really rich, possibly due to drilling the jets or could be floats or needle valves sticking. Carb kits specifically for the 400 are kinda spendy but here's a place you can get kits for other Hondas that use the same carbs for about 1/2 the money.

http://www.crc2onlinecatalog.com/Index_Main_Frame.htm

Read the message for 400s/450s down the page a ways.

There'll be more folks along with far more expertise than I have and they are very willing to help out.

Good luck, we'll be in touch. :D
 

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What makes you think that you needed to drill out the jets/go richer anyway??

Also check your timing and get it spot on, and do a compression check before spending any more money...


GB :mrgreen:
 

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Discussion Starter · #4 ·
i have a 88 P and 100 M jet to can swap which should be close....will probably have to get a bigger main but i should be able to get it to run enough to tune it.....

I'll have time to work on it tomorrow if i dont stay up too late tonight (card night) and i'll check compression and change the jets and make sure the carbs are extra clean which they should be since i totally took them apart and clean them very well...and if that doesnt help then i'll have to check the timing.....

another question.....if my cam chain is stretched then wouldnt that through the timing off a bit?....how to u know if its stretched?
 

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75/110 is quite a ways from 88/100 for jet sizes. :eek:
I'll be interested in hearing how this works for you as I will be addressing this issue down the road on my project. :)
 

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My 78 CB400T II has 75 and 105 jets (but I have no idea if that's stock or if the PO changed them for some unknown reason).

I recently got mine, am new to the forum too, and also trying to get it to run right...I don't have any help to offer, but I'll be following these threads.

Cheers,
BaileyMan
 

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Discussion Starter · #8 ·
i didnt get to work on the hawk but i did get to go ice racing on my TE510 !!
hopefull i'll work on it a bit tomorrow monring
 

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Discussion Starter · #9 ·
i played around a bit with the bike today....i have it running better with 88 pilots and 105 mains.....i'm hoping the local cycle shop has some jets for my carbs tomorrow....i'm going to purchase 115 and 125's and see what it does since its running lean right now but i think the pilots are close
i checked the cam timing and its spot on so thats good.

i'll report tomorrow!
 

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Discussion Starter · #10 ·
i was looking for the car assembly diagram on the manual and it show the main jet under the needle to be the smalle jet and the secondary main jet is the bigger one.....i think i have them mixed up if this is true...
 

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Discussion Starter · #11 ·
i now have the smalle jet unde the needle and the bike revs much nicer all the way to 10k rpms but the idle is horrible....with the butterflies 100% closed i cant get it to idle at all, not even a second...the pilot screws dont change a single thing...i can get it to idle better if i take the idle adjuster and start to opend up the butterflies but then the idle hangs in high rpms once i give it gas so thats no good.....i took the pilot screw out on both carbs and they look good...i put air to the pilot screw hole and the air passes to the venture with no issues......going to take the carbs out again and make sure the pilot idle circuit is good then see what happens
 

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The butterflies shouldn't be closed 100% at idle. Adjust the idle speed to 1200rpm then adjust the mixture screws. If you have vacuum gauges that's great, adjust for highest vacuum. If not just adjust to highest rpm. Then re-adjust idle to 1200rpm. Repeat as necessary. Personally, I open the mixture screws 1/8 turn from highest rpm/vacuum.

If you still have a problem with rpm hanging up it's being caused by something other than the idle circuit. I'm not that familiar with motorcycle carbs but I believe a sticky slider can cause this kind of problems. A vacuum leak is also a possibility but then you'll likely have trouble getting the idle adjusted.

May be a couple of real experts will stop by and offer some better help.
 

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Discussion Starter · #13 ·
i dont think its a vacuum leak i have new carb intake boots....the pilot air screws dont change the rpm at all!! i mean nothing on either carb......its the worse i've seen a bike idle in a long time...usually i'm pretty good about dailing in a bike but i feel so rusty with this one....

i'll take a loook at the sliders tomorrow so but they felt great last time i looked at them....maybe i'll stretch the spring some to apply more force for them to stay down.

i should have time to work on the tomorrow i'll let u know how it goes
 

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Discussion Starter · #14 ·
cleaned the slides really good and stretched the springs a bit and i would say it seemed to help a bit but still have a poor idle problem...my next step is to buy a carb synchronizer to see if thats the problem.
 
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