Topic: How to fit keihen carbs to a K7?

[CBK7CHOP]

Hi Folks and help.  I just picked up a project bike and I think the carbs I have are wrong.  But how can I get them to fit the head.  The engine in the bike is a K7 engine number 272....... The spare that was in the bike before engine swap starts engine number 100........ and I think the carbs came from that one. as I cant get them to line up.

The inlet rubbers are long and bend in, once fitted to the head the carbs 3 and 4 are almost on but 1 and 2 are out.  So tried to get a full set from the breakers to see if I could get a match, I got what I think is the right one's, still turn in but smaller, by ones I mean carb 1 and 2 so I need 3 and 4.

My questions are, Are these the wrong carbs? Has anyone fitted these carbs with matching rubbers to a K7 and can it be done using what model of rubbers.

Help please.

[CBK7CHOP]

Its a k7 engine with what I think are earlier carbs, keihen's with the nice choke leaver.
engine number starts 272....... which on the sohc web says its a K7.  I dont have old one's.  The rubbers were spilt because they were wrong and where taped up. 

[HondaMan]

You can get brand-new hoses (and I highly recommend it) today from Z1 Enterprises, online. You want the ones from the K1-K6 bikes, about $80 for a whole set. This will fit all those carbs from K1-K6, and even the early F0 carbs that are marked "7A" on the top of their tiny nameplates.

All of these bikes have the same head spacing for carbs, but the airbox (and its rubber hoses with their excellent internal velocity stacks) changed in 1976. You must use the earlier airbox with those early carbs or the hoses on the air horn side won't match up.

[CBK7CHOP]

Has anyone done what I am trying to do?  If so can you send pics?

[mrjack55]

Has anyone done what I am trying to do?  If so can you send pics?

The K7 came with Keihen PD carbs.  Yes they are different than the earlier Keihen's, but plenty of guys have swapped them out.  Listen to the words of Hondaman!  All you need is the proper boots for the carbs that you want to use.  If they are K1-K6 carbs get a set of boots from Z1.  Get that right, and they'll mount right up.  Then your next chore will be getting the air intake side of the carbs right.  Again heed the words of Hondaman!  You will need the right air box and boots (internal velocity stacks) for the carbs, not the engine.

I thought I had pics of a K8 that was running earlier (K1-K6) carbs.  But now I remember that it was pissing gas all over the place, and I didn't want to get to close to it. 

[Spiider]

Some re-installation tips once you have the right carb boots for those carbs.

Take the 4 new carb boots and install them to the engine first.

Rotate them to line them up, use a straight edge so they are all flat across the faces of the boots where the carbs will be pressed in next.

Check both across and vertically to make sure the face of the boots are all on one single flat "plane". 

Take a small amount of grease and put a thin film inside the openings so the carbs slide in easier.

The most difficult part is getting the carbs to press in to the rubbers.

Lots of tips and tricks for that in the faq section of this site.

I used a pair of large soft jaw wood clamps to squeeze both ends of the carbs with one jaw on the carb plate and the other on a 2x4 slid across the front of the frame at carb height. I had my exhaust off when doing this, so you may need to put something else across there to press against if you want to use my clamp idea.

Some people have had success with ratchet straps, or a rope somehow....find what works for you and doesn't damage the soft metal of the carbs or the engine fins.

Btw, in case you were wondering....they aren't going to slide on like magic, usually only hard work and cursing will get them on.  Don't give up, improvise if need be.

[CBK7CHOP]

Gents many thanks, I have had no help from Honda when called.  I am sure that the set of rubbers that I have are the ones I need, if I can up load pics of the carbs and rubbers can you guys give me the OK nod.  Hondaman many many thanks and the rest of you guyz.

[754]

Dont worry as much about the fins, as the carb throats, guys. When I worked with stock carbs which I dont really like.. got 1 nnd carb in first and next started, the pushed far side of rack while working up and down a bit. That was probably still soft rubbers back in the day, but I left the lumber for work, not for the carbs.
 For MR K7, I will make this simple;
 2 types of carbs you are like likely to run across, Fork tops (should have a rubber cover on them), and Coffin or flat tops.. no visible moving parts on top.. there is a third type with cables coming out the top , treat them as fork tops.
 2 types of rubbers, long ines that are angled, both ends look the same, and the other type, shorter, the ends are not the same.
 Basically, Short one MUST go with coffin tops. long ones with fork tops..
 IF the carbs are NOT marked KIEHIN, you do not have stock carbs..
 The above is all you need to know..

[CBK7CHOP]

Superb, the carbs i have have a locking nut at the top so I will treat them like fork Tops?  Once again thanks.

[Spiider]

The only thing I may add that I just thought of....if you use the "wiggling them on by hand" method as mentioned by 754, be careful you don't inadvertently push the bike forward off the side/center stand and have it fall over.

Very easy to do when you are focused on the carbs going in correctly and the amount of force to push them in is so high.

[754]

Center stand then block it aganst the wall, yeah it would suck if it fell .

[CycleRanger]

Don't pry too hard on the stay plate (the plate the holds the carbs) either!
It's aluminum and it's easy to break!
There are some threads about installing carbs.
Do a search and check out some of the pix.

[yellowbirdrs]

my K8 with early carbs.

[Don R]

I use a little silicone grease on the boots a 2x4 across the carbs and a tire iron inserted from the top using the frame as a fulcrum. CAREFULLY.

[CBK7CHOP]

Gentlemen, Last night I was out in good old Scottish weather, I got the carb rubbers on to the head, lined them up and for the life off me cant get the carbs to line up, this is after using a straight end... this is the longer rubbers that turn in?  3 and 4 line up the others are out by several mm? Also what a nice cafe racer... acn anyone send a pick if possible with the set up I am trying to do?

Thanks.

[754]

 If they are old rubbers they can be quite hardened, there are threads here on softening them up. Leave the part on the head unclamped so that they  can move around to find their way.. Did you lube both ends and the carbs?

[CBK7CHOP]

Well, I got home today, and I nuked them in the Micro went on the head a treat and got them have on all carb mouths.  Happy happy joy joy... Now for the last push, I am thinking rope and a metal bar, looped rope and twist twist to pop them on... You guyz are the best... 

[coldwave007]

I leave the boots attached to the carbs, only sliding them on/off the intake ports.  I use SylGlide - a sylicone grease - and lube up the inside of the boots and the outside on the intake ports on the heads.  Then put the bike on the center stand, sit on the thing, lock my feet in on the foot-rests, get one hand on the throat of the outer carbs carb, then push/wiggle them into place.  Works great!  Once you get the nack it's not bad at all.

And for what it's worth, I too replaced the boots.  The old ones were harder than sin.

[HondaMan]

Gentlemen, Last night I was out in good old Scottish weather, I got the carb rubbers on to the head, lined them up and for the life off me cant get the carbs to line up, this is after using a straight end... this is the longer rubbers that turn in?  3 and 4 line up the others are out by several mm? Also what a nice cafe racer... acn anyone send a pick if possible with the set up I am trying to do?

Thanks.

You may find that the #2 hose has to be turned a little, so the "2" on the top is not exactly on top, to get it to line up with the others: I've noticed this on most of the new hoses I've bought since 2006. I think Honda has a new supplier making them, and the #2 mold might be off a bit.

[CBK7CHOP]

Hi, very true.  I had problems with No 2, but bike now running superb.  1 problem is the return spring I can't seen to work out where it goes?  Also can some one tell me do I need a push and pull cable at all?

[Tugboat]

FYI the airbox may not line up exactly with the mounting tabs on the frame. I have the reverse: '76 F frame with the newer (77-78) carbs & airbox which doesn't line up. If you run into this situation, just zip tie them. Good luck!