Zephyr with idle problems

[91zedmonkee]

Hi Guys,

This is my first post on this forum, but I've read a few posts as a guest, and I'm amazed by the knowledge that gets around here. I've been slowly doing a custom build, and am 90% there with a few tuning issues to get sorted. I'm determined to get this sorted without resorting to a mechanic, because nothing beats fixing it yourself and knowing how to fix it next time...

I'm building a 91 zephyr 750 in a kinda rat / cafer racer style, and am trying to get it running without the airbox (k&n pod filters). It runs a bank of keihin CVK32's. I've been told that these carbs need good vacuum to really perform (which is hard to get without an airbox?), but I'll be happy to get it running smooth and properly. Prior to any changes to the carbs, without the airbox and with free flowing exhaust I was only getting 1/8th throttle before total loss of power (leaning out). No surprises there, so I ordered a kit for the carbs and fitted new main jets 122.5 on the outers and 125's on the inners. I shimmed the needles up with 2 washers, set the idle screws to 2 1/2 turns out, and took it for a spin (without filters at all because it's a hassle taking them on and off all the time). There was decent mid and top end power, but low end and idle were all over the shop. setting the idle with the throttle stop was near impossible with the idle racing and not settling. If i wound the throttle stop screw out to lower the idle it would drop for a few seconds, then get bumpy and slowly stall out. Whilst test riding I find it impossible to set the throttle screw properly, as to idle at lights i find a setting that works, but then when going up the gears as i pass through neutral it revs hard until i release the clutch and the engine load brings the revs down again. When braking and lowering the revs, at the lights again the idle is at a reasonable level, but slowly gets worse and would stall without a slight touch on the throttle to keep it idling.

I've cleaned the carbs as much as possible without compressed air, and have fitted new pilot screws and pilot screw o rings.

I'm certain the carbs are out of balance, but i can't get the idle consistent enough to do the balancing. I suspect an air leak, and the carb rubbers are quite cracked, so that's my next step. I suspect that carb manifolds which were borderline ok have been made worse by my removing the carbs so many times and are now leaking everywhere. I tried a wd40 spray test, but without much luck. I'm ordering new manifolds ($160 from the stealer) but I'm time poor at the moment and need to rule out vacuum leaks.

I am yet to test the float height (tomorrow's job) but would that cause an issue described above?

Whilst inspecting the carb manifolds I also saw some oil in the inlet ports on the head, so I'm thinking that I potentially have inlet valves that are sticking/staying open? I don't have a compression tester, but maybe I can source one tomorrow (an excuse to buy another tool!).

Some nay-sayers are telling me that it'll never run well with pod but I'm sure that heaps of bikes (some with CV carbs) run really well once setup right.

I realise this isn't really a question, and more of an intro / rant, but I'm really trying to wrap my brain around this problem and putting out some feelers helps. Any responders with similar experiences would be appreciated. I'll repost with some pics from the garage tomorrow and update with the float height settings and valve clearance / compression checks.

Cheers,

Bryan

[91zedmonkee]

Hey all,

So The idle problem has been kinda rectified, I replaced all the carb rubber boots / manifolds and can now get a steady idle. The jetting is still too rich across the board I suspect, due to high running temps. The plugs are light brown and performance is ggod, but I still have an idle between gear changes that doesn't settle down, so I'll try to shim the needles further and upsize the main jets by 1 size.

I've checked the valve clearances and all is well, so not sure what the brown residue is / was in the manifolds, but it has stopped occuring so I'll concentrate on other issues for now.

Once I have the jetting correct, I'll re-post with my findings.

Cheers all.

[kwakariderzr]

Hey mate
how did you get on with the idle problems. Bit late to post reply but only just saw your question,have had a Zephyr 750 for 19 years and encountered and fixed my share of small problems,
Cheers mate.

[Gosling1]

......Hey mate how did you get on with the idle problems. Bit late to post reply but only just saw your question,have had a Zephyr 750 for 19 years and encountered and fixed my share of small problems.........

mate, this bloke only ever posted twice and hasn't been logged on since January 2012.....I don't think he will be checking any replies

But I would like to hear of your experiences with the Zephyr 750. They were a very good if under-rated bike

[91zedmonkee]

Kwakariderz, I managed to get a win with the carb tuning. kinda. I replaced the rubber carb mounts and that sorted the air leak. Then I got it dyno'd and had the mains changed. That sorted the tuning issues across the board (and got me a good bit of poke too with pods and a 4-1 pipe), but I still had idle issues once it reached operating temp.

It's in the shop now and the mechanic tells me that it's an air leak past the butterfly's due to wear. He reckons try and find a new bank of good 2nd hand carbs.

Gosling, I have been lurking on the zephyr zone too, cos this project took a LOT longer than I envisaged. I finally got it sorted for a shakedown run in April '13 and I must say, I'm pretty pleased with the performance and delivery. The gearing seems a bit short on the highway, so I may change that up, but otherwise it's a really nice bike!

[Gosling1]

good to hear you have had some progress on this mate - getting CV's to work properly without an airbox to give a good steady source of airflow for the vaccum - is almost as much fun as poking needles into your eyes.

[ZephyrRider]

Hey Zephyr people , how ya doin, i checked back for a while with my post but nothing was happening so this i s first time i have been back. Great to hear you are getting somewhere with the carbs.
Good set on Ebay right now in the USA (bloody cheap with only 8,800 miles on them ) - problem is the postage cost. I got a good set with 50,000 km on them a couple of years ago from Sydney wreckers for $150 so hope you score a bargain. Will be keeping a regular eye on this forum from now on. I was kwakariderzr but i forgot my user , pass cause i didnt write it down.

[ZephyrRider]

gosling 1 wrote
mate this bloke only ever posted twice and hasn't been logged on since January 2012.....I don't think he will be checking any replies.

G'Day all ,not sure if last post is going through, how long does it normally take.
Can we post Pics on this forum, to show you my old workhorse.

[ZephyrRider]

this is why i didnt bother checking back last time, noone bothered posting back so once again i am think this is just like facebook - a complete waste of bloody time,
IS THERE ANYBODY OUT THERE ??????????????????????????

[Gosling1]

people are here all the time mate - they just don't always post an answer to every question.

Yes you can post pics - you can either link them from a host (eg Photobucket) - or just add the image in a post.

If you use the search function on the forum, there are plenty of threads with advice about how to add pics.

[ZephyrRider]

How are going with your bike now zedmonkee ?