Topic: Jetting for a Delkevic 4into1

[lash]

1972 cb750k stock engine. I have never used anything other than the stock exhaust so I am wondering if there is any difference in carb adjustments or jet sizes when running the 4into1. 

[BenelliSEI]

Interested to hear what others say. The Hindle system on my cb750F (stock airbox) is very similar and didn’t seem to need any changes.

[jaytee-nz]

Delkevic state that no jetting changes are required. I can verify that after fitting their CB750 system to my previous bike.

[beemerbum]

I installed a Delkevic 4 into 1 on my 1977 CB 750K7. I did not touch the carbs or change jetting in any way. Bike ran much better than with stock exhaust. Not to mention that it lost a lot of weight

[lash]

Thanks for the replies! It’s running rich now but I never set the engine up with any other exhaust so I will just carry on as normal. Kind of weird to hear only the one exhaust, I’m used to being able to tell which cylinder is doing what by which pipe!

[lash]

So I get the carbs apart and find out they have 115’s . Changed them to 110 and see how that goes.
Also, how do you jack the bike up to change the front tire etc.? None of my jacks work with these pipes in the way!

[M 750K6]

Can you get under the bottom of each side of the frame? I use a double width scissor jack with 'U's which fit under each side of the frame, while the bike is on the centre stand. Otherwise, tank off and a rope loop around the triple tree, so you can hoist it up a couple of inches on a roof beam, but not as solid that way.

[lash]

I have a scissor jack that has the u bolts for each side of the frame but they do not go high enough for the pipes to clear the jack. I am going to have to make up some longer bolts. Also don’t have any open beams to hang it from.

[gmet]

I had my engine rebuilt to pretty much 72 specs which is what my 750 is and I have that same exhaust. I started with 110 mains then went to 115s which was better then just swapped those out for 120s today and mister man what a difference. Thing pulls like a train now, little to no choke needed and great power. pulls so much better. I have stock air cleaner but cut the intakes back a bit to allow more air into the box, inside the snorkel area on the front and back. Love the sound

[Stev-o]

Also don’t have any open beams to hang it from.

A cherry picker could be used, maybe you can borrow one? 

[lash]

I don’t know anyone that owns a cherry picker! I am going to make extensions for my jack.

[CycleRanger]

Changing the oil filter can be a messy business as well.

[newday777]

I don’t know anyone that owns a cherry picker! I am going to make extensions for my jack.

Get hold of John's crew he had over tonight!

[Swoop]

I have a scissor jack that has the u bolts for each side of the frame but they do not go high enough for the pipes to clear the jack. I am going to have to make up some longer bolts. Also don’t have any open beams to hang it from.

Put them on a raised surface like 4x4 or 6x6.
I just put jack under 1 side but 2 sounds better

[HondaMan]

So I get the carbs apart and find out they have 115’s . Changed them to 110 and see how that goes.
Also, how do you jack the bike up to change the front tire etc.? None of my jacks work with these pipes in the way!

The K2 came with #110 mainjets (Keihin) until 3/72 builds, then it went to #105 mianjets. The cam changed a little bit in 3/72.
BUT - if the jets you removed happened the be Keyster brand, they run about 7% leaner than the number on the jet, as compared to Keihin jets.
For example: if you have a Keihin #100 mainjet and install a Keyster mainjet, it is the equivalent of a #93 Keihin jet.

So, don't let this bug confuse you. It has caused wars in some posts when folks didn't realize some are tomatoes and some are potatoes.

[lash]

My jets are keihins. I changed to the 110’s and did a clear line float balance but havnt had it out on the road yet.Yesterday was a solid rain day from the leftovers of Beryl. Going to take it out maybe tomorrow.

[newday777]

Interested to hear what others say. The Hindle system on my cb750F (stock airbox) is very similar and didn’t seem to need any changes.

John
The airbox of the F has a much bigger snorkel intake than the K models, about twice the size opening,  so that will have had a different effect of jetting.
Do you know what jets were in your F?

[newday777]

My jets are keihins. I changed to the 110’s and did a clear line float balance but havnt had it out on the road yet.Yesterday was a solid rain day from the leftovers of Beryl. Going to take it out maybe tomorrow.

Have you ever done plug chops to test the jetting? That's how I was taught back in the 70s by the guys out back in the shop to know if you have the jetting correct.

[lash]

No, trying to take a hot plug out of cylinder no.2 on the side of the road is not my idea of fun. The closest I get to that is running the bike down my gravel road from the highway for 2 km at around 4000 rpm and shutting it off in the driveway. Let it cool down and then check. Works for me.

[newday777]

It has to be done hot to get an accurate testing. Look it up how to do it properly.
Wear gloves.

[willbird]

It has to be done hot to get an accurate testing. Look it up how to do it properly.
Wear gloves.

I am a little skeptical there...I'd have to see plugs pulled scorching hot set side by side with plugs pulled stone cold and see a dramatic difference to buy into that one :-). I like learning things tho :-). The guys reading plugs on 3500hp V8's say you have to cut the plug apart to get a "real" reading too, looking down into it is not good enough according to them.

[newday777]

It has to be done hot to get an accurate testing. Look it up how to do it properly.
Wear gloves.

I am a little skeptical there...I'd have to see plugs pulled scorching hot set side by side with plugs pulled stone cold and see a dramatic difference to buy into that one :-). I like learning things tho :-). The guys reading plugs on 3500hp V8's say you have to cut the plug apart to get a "real" reading too, looking down into it is not good enough according to them.

Well those that wait until the plugs cool off are most likely not doing the plug chop then as you have to get it up to the rpms, hold it and kill the motor coasting to the side to get an accurate reading. No idling or changing rpms.
But you do as you will.... Results will vary that way.

[lash]

Oil thread!

[willbird]

It has to be done hot to get an accurate testing. Look it up how to do it properly.
Wear gloves.

I am a little skeptical there...I'd have to see plugs pulled scorching hot set side by side with plugs pulled stone cold and see a dramatic difference to buy into that one :-). I like learning things tho :-). The guys reading plugs on 3500hp V8's say you have to cut the plug apart to get a "real" reading too, looking down into it is not good enough according to them.

Well those that wait until the plugs cool off are most likely not doing the plug chop then as you have to get it up to the rpms, hold it and kill the motor coasting to the side to get an accurate reading. No idling or changing rpms.
But you do as you will.... Results will vary that way.

IMHO it is a little tough to do a plug chop at 2000+ HP on an engine dyno LOL.

They do a pull and get it shut off and then do a plug read. Timing they are looking at how far the plating burned off the ground electrode, color they cut the plug shell off and look at the insulator.

They usually have EGT and wideband readings to look at as well. Typically not going to the ultimate potential of the engine on the dyno either.

Bill