X6 Hustler Bogging at Speed

[Suzukidave]

Checking carb operation chart it looks like it could be in the needle jet and pilot jet area , did you remove and clean the needle jets and and pilot jets when you cleaned the carbs ? But why it only des this when the bike warms up is a baffler

[Tourmaster]

Yep, the carbs have been cleaned and checked twice. First time with the OEM 95 main jets installed, and then again when I installed the 90's. Even double checked the float heights and made one slight tweak.

For the test run this morning, fired the bike up with one kick. Within about 5 minutes, had the bike out on the main highway and smoothly up to 70 mph with lots of power. After a couple of miles of steady/strong running, pulled off onto my local paved back road to continue the test ride. After another 2 - 3 miles down that road, cruising at over 60 mph ... the bogging gradually started to take effect. I could actually downshift into 5th and squeeze a bit more speed out of her, while pushing the revs up into the 6000 rpm range, for example. But eventually (as the heat rises) even this move brought diminishing returns as the cruising speed (>55 mph) bogging became more prevalent.

All I have on my "easy stuff to do list" at this point is replacement of my carb insulators, and perhaps lowering my needles a notch. As always, alternative suggestions are always welcome. Dave, thanks for the input today .. much appreciated.

[tz375]

If it started to heat bog after just a few minutes I would have suggested that it's too rich at some part of the scale and probably on the needles/jets as Dave suggested.

The fact that it takes a bit longer tends to suggest that the motor is getting hot and there's some sort of heat soak effect. Those motors used to have a problem in race trim with heat causing all sorts of problems but you're not in TX in the summer riding wide open.

The other possibility is the float bowls running out of gas as you run it hard. That might be a partial blockage in the petcock or maybe some casting flash in the fuel feed side of the carbs. Pull the fuel hoses off the carbs and turn the fuel on and let it drain into a large fuel drum. Look at the flow rate and see if it's really slow or starts to slow down after a while.

Next trick is to pull the float valves out of the carbs and make sure the drillings are all clear. I like to take a 3mm carbide rotary burr to the feed system to clean it up and port it. A simple way to test them is to remove the float bowls and turn on the fuel and see how fast it flows out. Obviously do that outside and in a way that collects the fuel that's draining out.

If that all checks out, you can try with the needles one clip position lower and one higher and see if that changes anything.

Next after that is to try better fuel or try with a couple of degrees less advance and see if either of those makes much of a difference.

Do you have access to a CHT gauge or laser pyrometer. Go for a run and see the temps and see if they increase as the thing starts to bog. Typically detonation causes a rapid increase in CHT and lower pipe temps.

BTW, do you check plug color after a high speed run or after you nurse it back home?

[Tourmaster]

Early on, I had been having issues with the original petcock, but have since replaced it with a new aftermarket unit which flows much better. With the old OEM petcock, I could actually see pockets of air in the clear fuel lines. With the new petcock, the lines are always full. I'll pull the carb lines and run a full bore, longer duration flow test as you suggest. The float seats and needles are new replacements and my earlier test flushes through the carb fuel port to the seat port all flowed very well.

On the fuel flow front, at this point I'm most suspicious of the carb insulators. When the bike gets hot and exhibits the bog blues .. I can see air bubble heading up out of both float bowls towards the petcock. Others have suggested that these old insulators lose there effectiveness, resulting in fuel boiling a bit in the bowls as the engine get hot. Just haven't got the new insulators yet, as up here in Canada they usually come by dog team. Dealer says they should be here in about another week.

Not sure what specifically you are suggesting I will learn using a heat gun to monitor engine temp? I know that as the bike warms up ... and as it gets hotter, and hotter, the bogging issue becomes more and more pronounced. Is there is something additional I will learn by knowing precisely what the cylinder temp actually is?

With regards to my plug coloration ... during my last test run, I chopped the throttle off at 60 mph, shut the engine off, and coasted to a stop. The left plug was a medium brown, and the right plug was slightly darker brown ... no soot on either.

Again, very much appreciate the comments and ideas.

[Suzukidave]

Sorry to keep asking this same question but i think it needs to be clear that you did indeed completely remove out of the carb the needle jets and pilot jets as with these small carbs it doesnt take much to plug the small holes along the sides of these jets . Just flushing out with them still installed in the carb body may not clean them out .

[tz375]

@Suzukidave, Good point. And needle jets are often partially clogged around the spray tube.

In terms of temp. the temp will rise to say 200F and if it stays that way then it's probably not a heat soak issue. If it's say 200 after a short run at WOT and rises quickly to say 300 as it starts to heat bog, clearly the issue is heat causing a slowdown or something causing a heat rise.

Once the bike stops, engine temps continue to rise as heat is no longer being carried away by the airstream.

[Vintageman]

Some more other ideas.

Did the X6 come with a Hex main or Round main jet Factory? If it was hex (for example I think older 1968 T305 was actually hex and later t350 were all round). If it is to be hex and you put a 95 round (yes it screw in real easy too, can’t tell that way If wrong) it is like a 105 hex. Just a thought

Bog: Please describe some more: tough to do I know. For example I am thinking when it get hot you open up the throttle it just slows down? Does the combustion go quite (cuts out), Still some power but very little. Does it ever pop or bang out of exhaust or intake?, When it loses power if not completely quit is it a bit gargling sounding
Also, when hot does it still start easy and say first kick or you have to kick it a lot to get it started again?

The other ideas are electrical: If your condensers are week and get hot that can be a problem. Also same with coil getting too hot. Good spark plug caps? Ohm things out measure capacitance of condensers or change if old. Also make sure you have sufficient dwell (time points stay closed), If you gap too wide the coil will not have time to saturate and give week spark

I do agree, Make sure you pull out needle jets and check for blockage at air jet. Also look inside the barrel. It should be smooth, if not shinny or dull like the surface of the moon. If rough the fuel does not atomize and more droplets, usually a problem midrange but WOT usually OK? Also end my be egg shaped not round where needle travels. Does the jet needle have wear?
Verify right Needle Jet and Jet needle. Who know if some had changed them at one time. Also Needle Jet series will tell you what type main jet


Good luck

[Vintageman]

Some more other ideas.

Did the X6 come with a Hex main or Round main jet Factory? If it was hex (for example I think older 1968 T305 was actually hex and later t350 were all round). If it is to be hex and you put a 95 round (yes it screw in real easy too, can’t tell that way If wrong) it is like a 105 hex. Just a thought

Bog: Please describe some more: tough to do I know. For example I am thinking when it get hot you open up the throttle it just slows down? Does the combustion go quite (cuts out), Still some power but very little. Does it ever pop or bang out of exhaust or intake?, When it loses power if not completely quit is it a bit gargling sounding
Also, when hot does it still start easy and say first kick or you have to kick it a lot to get it started again?

The other ideas are electrical: If your condensers are week and get hot that can be a problem. Also same with coil getting too hot. Good spark plug caps? Ohm things out measure capacitance of condensers or change if old. Also make sure you have sufficient dwell (time points stay closed), If you gap too wide the coil will not have time to saturate and give week spark

I do agree, Make sure you pull out needle jets and check for blockage at air jet. Also look inside the barrel. It should be smooth, if not shinny or dull like the surface of the moon. If rough the fuel does not atomize and more droplets, usually a problem midrange but WOT usually OK? Also end my be egg shaped not round where needle travels. Does the jet needle have wear?
Verify right Needle Jet and Jet needle. Who know if some had changed them at one time. Also Needle Jet series will tell you what type main jet


Good luck

[Tourmaster]

Dave ... with regards to your question, all brass carb components were completely removed. Initially the prime plungers, pilots, float seat and needle were replaced with new Wemoto kit items from England. These items all appeared identical to the original components that were removed. All orifices were inspected ... including the side ports, prior to installation. The main needle jets (95's) were soaked overnight in carb cleaning solution and reinstalled initially. As part of my test process, as I've mentioned earlier, I later replaced these jets with the Wemoto kit jets (90's). This step improved performance a bit, and eliminated the sooty appearance on the plugs.

Vintageman ... the original main jets, as well as the subsequent Wemoto jets are both hex type. Both look identical, other than the orifice size. I still have the original needles installed, but am thinking about trying the Wemoto needles that were supplied in their kit ... also plan to play around with the needle height, as I mentioned earlier ... and was suggested.

Bog description ... well, when it starts happening, it's like the brakes start dragging once I reach about 55 - 60 mph. When the bike is fully heated up, if you keep pushing the throttle in the bog zone, the bike does actually start to slow down a bit. Combustion is still happening smoothly, but is lack-luster. There is never any popping or banging out the exhaust side ... or "gargling". Even when the bike is hot ... for example, when I did the plug chop check today ... the bike fires right up again. Also, when the bike is fully heated up ... I can ride around all day with no problem, as long as I stay in the < 55 mph bog zone. Engine is a little less responsive once warmed up, but still cruises and accelerates quite well.

As mentioned earlier, new plug caps have been installed. It was mentioned to me that the condensers are probably okay, since the bike is not missing when the Bog occurs. I've place a set on order, just in case though.

[Suzukidave]

" all brass carb components were completely removed " this included the needle jet ? I ask because i had completely cleaned a set of GSXR carbs lately but when i removed the needle jets to replace they were dirty and clogged

[Vintageman]

Very good.

One more question about the bog: 55 - 60 mph. Is it throttle position related? I mean if you are on a flat 6th or 5th gear your should be able to do 55-60 mph tail wind, at say less than half throttle. Or if you say it is throttle position related now say you are in 4 th climbing an 8% grade 40-50 mph and then go to the throttle position problem area will it still occur?
Usually jetting is more throttle position related not so much your speed or RPM, but the loading can be it light or heavy tends to expose jetting issue more readily.Also hear change in combustion sound even if subtle. N change in sound but like brake being applied is not typical

I would have gone with OEM jet only. You doubt them once issues like this occur even though may not be it.

For example if you look at T350 history they changed jetting and kits (Keyster) is only forthe early one and kit not complete (no Needle jet for example which is one thing that changed and they do give a new jet needle which is wrong for the later needle jet).

If electrical yes usually pops or misses. But if dwell too short worse at RPM or hot, but sound change I think. Timing off won't pop just no power, maybe worse hot not sure. If advanced too much it may ping, but I think that has squish heads so hard to hear that if at all

If it is heat problem it should get worse with loading of engine. I mean if you are 60 mph on a flat it happens hot it should happen at 40 mph if you are climbing a grade for a time. Change of 10-20F in ambient air doesn’t help much if a true heat problem. Have worked on snowmobiles from the late 70s that were fan cooled and choked by the cowl design and would act as you say particularly when trying to get them to climb a grade. Take off hood no problem. But don’t think X6 had a heat problem, unless someone shaved the head trying to raise compression? However Suz did add more head cooling abilities with later designs.

Mechanical. If it starts first kick when hot then sounds like good compression ring seal. If the engine idles well doesn’t rev up, stall or variant sound like some seals are decent. Also no heavy crankcase oil smoke from leaky center seals?
The only other issue carbon plugging cylinder ports exhaust or transfers. It is not too hard to pull of the heads and take a peek inside. Don’t have to remove carbs or exhaust or jugs.

Are the brakes dragging or wheel bearings. Did you feel the wheel axles or drum for heating. Chain?

Funning my R5, I tighten rear brake and if the suspension dipped at all due to road or accelerating hard rear brakes came on

So Fuel, Electrical, can't shed the heat, or mechanical. Can't say which for you. Isn't vintage fun

[Tourmaster]

Vintageman ... my brakes, wheel bearings and chain are just fine ... just trying to find some way to answer your question and describe how the bike feels when the bog occurs. The engine sound does change when bog starts ... like the engine is starving for fuel a bit.

Sorry, no hills around here ... I live in pancake land (Saskatchewan). However, when riding against the wind, the bog begins a bit earlier on the throttle position. Yesterday when I did the throttle position test suggested by Dave, the wind was fairly calm ... so no appreciable head/tail wind.

Negligible carbon build up throughout ... and exhaust system is clean and clear. Bike idles fine when cold ... when hot, requires a bit of throttle nursing when coming to a stop, for just a few seconds, then also idles fine.

Am off to another vintage bike rally for a few days. Will get back at the last few tests, suggested by others previously, probably next week. Will update y'all then. Would like to get this final issue sorted, before tear down for chroming and repaint this fall. As always, very much appreciate the comments and ideas.

[tz375]

Good ideas from Dave and Vintageman.

The smooth bog - no misfires suggests it's not electrical. Condensers usually just go open or closed circuit and fail when hot, but it's a cheap fix. If you can't find exact replacements, almost any condenser will do and can be mounted on the points plate or beside the coils as Honda used to do. It's worth replacing them just to be sure.

The needle jets are probably PRIMARY types which are less prone to clogging, but they are worth checking. I didn't see them mentioned in your list of parts cleaned or removed.

The fact that it fires right up after a plug chop suggests either the float bowls filled up while it sat or that it's a jetting issue. It also suggests that the motor did not tighten up which is how it sounds. If it turns over freely after it goes flat, it may be hot, but it's not getting tight. Fuel may be boiling off though so it will be interesting to see what happens with new insulating blocks.

At 55-70 bikes are usually running around 1/2 throttle, and sometimes less than that, so I'd try moving the needles to see if that makes a difference. Drop it one clip position (clip up, needle down) to lean it out slightly and see if that cures it. If not, try moving it the other way.

Another crazy thought. I wonder if insulation is breaking down in the alternator stator windings leading to insufficient output which on some bikes manifests itself as poor running at higher revs when hot. Take a multimeter and test the battery voltage with bike running normally and after the sag at say idle and 4000 rpm. The reason I came back to that is the old rule of thumb: If you are 100% sure the problem is carburation, it is most likely to be an electrical fault.

[Vintageman]

But do you think it is it throttle position related? Usually your not that unlucky and only one jetting circuit is out of kilter not all. Float level good affect all
If carb jetting try from low RPM and climb in rpms all why holding a fix throttle position (1/8, ¼ ½, ¾, full ). If a circuit is out it should show up

If you think it is lean apply a little choke (very little , it can be done, be careful). If it dies out not lean. If it is bogging at 60 mph full throttle back off to 3/4 throttle. If it gargles backing off too rich WOT, if it runs better too lean WOT


I am with Tz: You think your carb is rich its lean, you think it’s lean its rich. You think its carb it’s electrical.

Coils of wires separated with insulator material be it Stator or Ignition coil when hot (material expansion) one of the many winding loops may touch/short. Ignition coil worse due to high voltage arching even if not direct touch. This would be more RPM related. Try another ignition coil for example

It does sound like some item carb or electrical is affected by heat. No gear train noise I presume when hot either

Well your sure have a lot of ideas thrown at you from us.

I'll stop throwing my 2 cents out (for now). But very intersted to hear what you learn or find out

[Alan H]

Couldn't be anything a silly as a bunged up fuel cap breather hole could it?