| Archive for hondacb400.myfreeforum.org Motorcycle forum for ALL Bikers |
| honda |
bike wont go over 65mphBought cb400sf last year its a 1993/4 model it was imported to uk in 2000,iv had it out on the road a few times and each time it starts to top out at 65mph and with a back wind it will touch 70mph,although it soon drifts back down to 65mph,the speedo reads in kph. so at this rate im thinking well i might as well have bought a honda 125cc. Also the cb400sf will start to cough and splutter when maximum velocity is reached although it will run as smooth as silk up to 65 then cough and splutter so i lay off the throttle slightly down to 60 and smooth again then full throttle reaching 65 and splutter then lay off throttle and ok again ,you get the picture . so i was wandering is this the end of the line and should i sell the bike and get somthing faster or is there a way round it by altering somthing mechanical or electrical ,has anyone gone through this with their bikes here . |
| honda |
i forgot to mention above that i have already converted the kph to mph figures so 65mph as stated reads 104 kph and the speedometer is in kph,confusing! 
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| admin |
sounds like you've got quite an issue there!
When was it last serviced? Does it revv all the way to redline? How does it sound when running? lumpy? Is it running on all 4? They are good for 120mph so, it sounds like it needs some attention. |
| honda |
maybe electricalhi , i serviced the bike when i bought it last summer ,it got new spark plugs, oil,coolingsystem flushed and new coolant,2 new tyres also new sprockets and `did` chain. when i first got the bike it was a bad starter and after new spark plugs it fires up on tickover first time. the bike itself the engine runs without the slightest glitch theres no uneveness to it ticking over right through to the red line which i tested if it would red line today and after warming the engine it did go straight to maximum revs 14000rpm , today i took off the end spark plug cap on the gear change side and started the bike again `to check if all the four pistons are receiving a spark and running proper` and there was no difference in performance the bike still started fine and run like a finely tuned engine like it always does,so i removed the spark plug cap next cylinder and now there is two spark plugs without any connection to the electrical system and there was a noticable lumpiness to the engine sound ,so to sum up - on three cylindres theres no change but on two cylinders there is a spluttering sound. i think i have an electrical problem by the sound of things ,i will have to investigate further ,you may have solved my problem when you mentioned is it running on all 4,so i appreciate your help ,ill post my findings soon if spare time permits me to do some work on the bike. |
| admin |
no problem glad to help out,
if you get stuck let me know. Try that meathod on all 4 cylinders, it could still be running on 2. It could even be split carb diaphrams? good luck |
| super 400 |
Sounds to me like you have a broken down coil, which you can test with a multimeter. Does it pull well all the way upto 65mph, i had a similar problem but mine was a restriction on the cdi which wasn't letting it go past 5500rpm which the resistor mod fixed. |
| honda |
check coilthe first thing i shall do is look at the spark plugs and see if the electrodes are oiled up on any one of the 4 plugs,if so i will back track along the high tension leads and put a multimeter to the coils ,i have some spare ht lead so i will change them first off ,I spoke to the local cycle shop also and they said change your spark plugs and ht leads first,i have already changed plugs when i first got the bike ,so the ht leads and coil are next up,much appreciated, thanks. |
| honda |
still unresolvedhad the spark plugs out and theres a good spark on all 4 plugs so it cant be the high tension leads or coil or any of the electrical system that isnt working,i have taken out the carburettors to check for reduction sleeves in the intake and or outtake ports and found nothing there that shouldnt be there ,as i am getting the full rev range on the rev counter i didnt think there was a problem with carbs but i checked anyway ,i have the speedometer in bits now to see if theres any speed limiting gadgetry in there but have left it at that for today ,i cant seem to get past the lifting out of the dial and unit as the reset dial knob seems to be impossible to remove and it has to come out so i can lift the workings out ,all day in a cold garage and still no further to finding the cause.iv done a lot of trawling the net for a spark of insight into the problem,i found the irish biker forum with lots of posts but nothing in the line of 400cc bike wont go over 65mph,just some carb freezing issues and holes in diaphragms . |
| honda |
iv just found a thread on on air flow restriction what do you think.
http://answers.yahoo.com/question/index?qid=20081224071841AAMW2gO |
| admin |
dunno about that link.
You mentioned changing the plugs before, and now you say you have spark on all 4. When you changed the plugs the first time, did you have the HT leads on the wrong cylinders, (its unlikly, but some mechanics do it.) Have you checked the air filter is clean and not really dirty. Do a compression test on the cylinders. Maybe your main jets in the carbs are blocked? the 400 doesnt have any restrictors in the carbs, (unless its a 33bhp restrictor but it should still do 100mph.) (that link is for a moped anyway) Concerning the speedo restrictor. No i cant seem to remove the needle either. The best thing to check is that the block connector on the back of the speedo, if its connected and the fuse that controls the dash isnt blown (taillight, horn, indicators, brakelight, meter, fuse.) then this wont be the problem. |
| honda |
carbsi will get a compression test done but im going to have to leave it until last resort as it means taking bike to garage ,ill have the carb cleaned out whilst they are of the bike i will take to bike shop its £60 here for strip down and clean ,they may well find a blocked jet.I knew the link was for a 250cc scooter but the principle of there being a restriction to the air intake pipe to the petrol tank under high intake pressure say when reaching speeds of 65 mph may well stand also for a 400cc motorbike especially if the petrol tanks gauze filter has any build up of say rusty sludge on it which would exagerate the restriction even further,i havent checked the tank for this yet and will be doing so though . i dont use the bike a lot mainly a treat in summer after work to have a ride,i dont mind travelling at 60/5mph its just when you get on the main roads every thing on the road is going 70/5mph. |
| honda |
i put the bike back together and will let local cycle shop to fix.Only now it wont start at all the batteries run flat and so has my enthusiasm for the time being ,ill get back to this forum within the next 6/12 months when its all sorted out ,its just one thing after another with this bike ,thanks for your help and sujestions.
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| admin |
no problem,
hope your back on the road again soon. 
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