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trumpetsandjampots
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Posted: Wed Sep 10th, 2008 04:07 pm |
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Hi all
Quiz time but I don't have the answer.
The Honda CB 350K series engine is used in classic racing, how much to buy one in fine fettle?
regards Rob
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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NickR
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Posted: Thu Sep 11th, 2008 12:31 pm |
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If you want it to be competitive, I'd have thought a couple of grand.
Have a look at the ads on the CRMC website.
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The older I get, the faster I was.
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trumpetsandjampots
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Posted: Wed Sep 17th, 2008 12:33 am |
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Now watching a very pretty bike (350 K4) on Ebay............. even my youthful son thinks classic racers are cool..... cant afford it mind you!
Day dreaming about a clean fast line through the veranda.
Rob
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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jamie.s
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Posted: Wed Sep 17th, 2008 08:39 am |
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trumpetsandjampots wrote: Now watching a very pretty bike (350 K4) on Ebay
Seen that the other day, looked a nice bike.
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15 years old! Bikes: 1956 Ariel Colt TLR200 2X cb550s, D10 bantam trials, 2000 ER-500 Kwak
My bike in CBG magazine
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racerd
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Posted: Mon Sep 22nd, 2008 06:36 pm |
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have you tried tuning the engine your self
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trumpetsandjampots
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Posted: Tue Sep 23rd, 2008 12:30 am |
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racerd wrote: have you tried tuning the engine your self
Hi there i was wondering what can be done to perk the little honda up for faster road work. No doubt you can go large and Hales Hondas seems a great place to start if wanting something for the weekend.
Perhaps my ideal would be a compromise but I imagine getting it spot on with matters like ignition (possibly electronic) and better carburation (ditch the diapragm carbs) are useful starting points.
In other words make it breathe easier.
Has anyone had any experience with building these in mild state of tune.
regards Rob
PS even bare engines seem costly to play around with.
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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dudley472
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Posted: Tue Sep 23rd, 2008 09:19 am |
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| i used to race a k4, a top spec motor can cost a whopping 6k, to make a stock bike reasonably fast you will need to bore it out to a genuine 350, they are 325 as standard, you will then need to change pistons omega are the best but they cost £500 a pair, an alternative would be gpz750 jobbies which fit, you will need a cam, megacycle and joy make these.....not cheap though, you will need to uprate the camchain, one from a 750 4 will do, tensioner will need to be changed the head wil need sorting to flow better , take the alternator off to reduce weight and get a self generating ignition again about £600 you can run total loss with a boyer though, you will need to change the pipes, swarbrick are the best and cheapest at about 400 quid a pair, some guys use gibsons which are quite expensive, this is absolute minimum as far as the motor goes, these things are pretty fast, as far as carbs go i had amal mk2's but most people prefer mikunis Attachment: k4-1a.jpg (Downloaded 54 times) Last edited on Tue Sep 23rd, 2008 09:25 am by dudley472
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trumpetsandjampots
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Posted: Tue Sep 23rd, 2008 12:36 pm |
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hi Dudley
Smashing info, it certainly sets out a useful starting point. i can see creating a quick one requires very deep pockets, minne are rather shallow at the moment but the trick with the gpz pitons and acarb change is at the economy end. i assume the head will need the combustion chamber slightly modified for clearanes and adjusting the comp ratio.
Obviously getting the fuel air mixture in and out becomes the next issue, cams is one way and I see Hales do a larger valve, have you done work on the inlets to reshape or were they just cleaned and blended to the new carbs. Exhausts? keeping it all road legal might be a barrier.
Cheeky I know but these little bikes are impressive on the road circuits andits good to chat with someone with experiences of tuning rather than read it in a mag.
many thanks Rob
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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dudley472
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Posted: Tue Sep 23rd, 2008 12:53 pm |
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I ran standard valves no problem and pretty much a stock head, just cleaned up a little, you can spend loads on race valve springs but standard ones from david silver are fine i just changed them every season or when one broke which ever was sooner, the race ones brake as well........ the chain tensioner is quite important as the stock rubber wheel brakes up and clogs the gauze oil strainer resulting it serious damage, the crank can be lightened and balanced but they do vibrate a lot when this has been done. for a road bike i would get
Pistons probably gpz cos they are cheaper
cam you need this without doubt i had a joy 254 in mine, this makes the bike come to life
carbs, i has mk2's at 32mm they say the best is to buy 30mm and bore them out to 31 as this is optimum but 32's seemed fine to me
exhausts, the swarbricks with baffles in are what the racers use and are not that loud they will go through a mot due the the age of the bike, this is what you can see on my bike they sound fantastic and they were the same as on the works bikes of the day
brakes, the bike will be quite fast with this lot on, a front end fom a 400 four is what i had, some people went a bit bigger and had a 550 four fron end, i had a cast iron disc from C.A.T racing
http://www.cateng.co.uk/
hit the link that says cat racing, they do some great stuff but they are the people that will charge 6000 quid for a motor wow
Last edited on Tue Sep 23rd, 2008 12:54 pm by dudley472
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trumpetsandjampots
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Posted: Thu Sep 25th, 2008 11:57 pm |
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Cheers Dudley
Thanks for another useful link. it all makes for very interesting reading and really makes you aware how much scope there is with these bikes.
Its funny, when I hooned around on a CB 350 back in 1977-78 I never thought it was such a useful bike for tuning. Quite clearly I had missed the point but I suppose these were the days of 'spannies' and porting on the stinkwheels so the oddities such as the 350 k4 were nothing special. I suppose their current popularity for classic racing is because other that the brits they were the only Jap Four stroke twin just under 350cc.
The bottom end was rock solid and they took abuse (thats my own experience of jumping ditches on Cooling Marsh).
Question: can the CB250K4 engines be tuned the same way and taken out to the larger size with barrel and heads? I just happen to have a spare in the garage to play with?
best wishes and thanks again
Rob
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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dudley472
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Posted: Fri Sep 26th, 2008 07:19 am |
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| the engines are virtually identical, some racers use 250 cranks as the rods are lighter, others wouldn't touch them as they say the rods are weaker, i ran 250 ods for 3 years no trouble, you can put 350 top end on 250 cases no problem, the reason they are so popular is they are eligable for classic racing simple as that, someone read the rule book and found that nowhere did it say your pre 72 bike had to be british...... this caused a bit of a stink at first and many people are still very much against them now, but if you want a fast 350 it has to be a k4, some people claim nearly 50 bhp i doubt this but you never know and they jst rev and rev mine used to go off the tacho (12000) in top down the railway streight at aintree god knows what it was reving too but it just kept making power, until a valve spring broke this is the only problem i ever had, it just used to break one once in a whileit was a great bike wish i'd not sold it really, i went on to race a weslake triton, tasty but not so much fun Attachment: race1.jpg (Downloaded 35 times)
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trumpetsandjampots
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Posted: Fri Sep 26th, 2008 08:11 pm |
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Hi Again Dudley
I guess that confirms my thoughts of one of the few eligible bikes and explains why I had to spend more from my piggy bank than expected to get one. i saw an Incomplete 350 motor make over £300 on ebay recently but it had head and barrels so was a god starting point from what you say.
Sometime over the winter I will be peering inside my engines and deciding where to go next. I'm getting a bit lardy for classic racing, or any form of racing so if i choose to follow your spirit my son can be the jockey.
He can ride bloody well, he has taken my old firestorm and rode round much faster bikes on track days at Brands so he would not take a lot of coaxing.
Well thanks for all the tips and giving me an idea of the scope of modifications now its time to browse the websites and see how much we need to save. (or sell to raise funds)
Cheers Rob
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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dudley472
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Posted: Fri Sep 26th, 2008 08:29 pm |
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| we used to buy engines for 50 quid a pop, a guy bought a container load from the states where the bikes were much more popular than they were here, i sold my bike a couple of years ago i sold it for 2500 included in that was my spares stash which included 6 complete engines all stripped cleaned and assesed and 3 frames with v5's prices have gone mad, no such thing as cheap racing, i have stopped racing classics now as the costs are so high, i have a sv 650 minitwin all i have to do is change the oil and put petrol in it, i don't even take any tools to meeting anymore
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trumpetsandjampots
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Posted: Fri Sep 26th, 2008 08:41 pm |
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I understand why, nothing stays cheap for long particularly where obsolete machinery is involved.
That container of engines would fetch a pretty price today. good luck with the minitwin, hope it stays rubber side down.
regards Rob
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winters coming: sidelights officer? no thats main beam.
TR6, G80S, Plunger T20,Honda VTR1000,CB350 K4
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